7d7bf2f build: set minimum supported macOS to 10.12 (fanquake)

Pull request description:

  Extracted from #16392 as this doesn't need to wait for the other build changes.

  Reasoning:
  * `10.10` has been unsupported since July 2017 (~3 years at `v0.20.0` release)
  * `10.11` has been unsupported since July 2018  (~2 years at `v0.20.0` release)
  * macOS users are consistent at upgrading to new releases.
  * Qt 5.12 LTS only supports [macOS > 10.12](https://doc-snapshots.qt.io/qt5-5.12/supported-platforms.html). As long as we're supporting macOS < 10.12 we would not be able to bump Qt in depends to 5.12 for the `v0.20.0` release.

  Once we drop support for 10.12 and start using the 10.15 SDK there are some other follow ups:
  * Enabling support for [`thread_local`](https://github.com/bitcoin/bitcoin/blob/master/configure.ac#L901).
  * Removing some of the macOS notification code
  * Removing macOS [startup item code](https://github.com/bitcoin/bitcoin/blob/master/src/qt/guiutil.cpp#L695).

  There was also some related discussion in the `#bitcoin-builds` channel yesterday arvo.

ACKs for top commit:
  laanwj:
    ACK 7d7bf2f
  dongcarl:
    post-IRC-grilling-ACK 7d7bf2f

Tree-SHA512: 30b0ed75e3b4df2d3f94db2091b7982c1ea7be8fb3a2732d8efd1a53ef1e492d7265a47e90c38e92f66e638d10e9400a6ecb56e5093688bb26d1621645b453e8

7d7bf2f build: set minimum supported macOS to 10.12 (fanquake)

Pull request description:

  Extracted from bitcoin#16392 as this doesn't need to wait for the other build changes.

  Reasoning:
  * `10.10` has been unsupported since July 2017 (~3 years at `v0.20.0` release)
  * `10.11` has been unsupported since July 2018  (~2 years at `v0.20.0` release)
  * macOS users are consistent at upgrading to new releases.
  * Qt 5.12 LTS only supports [macOS > 10.12](https://doc-snapshots.qt.io/qt5-5.12/supported-platforms.html). As long as we're supporting macOS < 10.12 we would not be able to bump Qt in depends to 5.12 for the `v0.20.0` release.

  Once we drop support for 10.12 and start using the 10.15 SDK there are some other follow ups:
  * Enabling support for [`thread_local`](https://github.com/bitcoin/bitcoin/blob/master/configure.ac#L901).
  * Removing some of the macOS notification code
  * Removing macOS [startup item code](https://github.com/bitcoin/bitcoin/blob/master/src/qt/guiutil.cpp#L695).

  There was also some related discussion in the `#bitcoin-builds` channel yesterday arvo.

ACKs for top commit:
  laanwj:
    ACK 7d7bf2f
  dongcarl:
    post-IRC-grilling-ACK 7d7bf2f

Tree-SHA512: 30b0ed75e3b4df2d3f94db2091b7982c1ea7be8fb3a2732d8efd1a53ef1e492d7265a47e90c38e92f66e638d10e9400a6ecb56e5093688bb26d1621645b453e8

The macOS startup item code was disabled for builds targeting macOS >
10.11 in bitcoin#15208. Now that we require macOS 10.12 as a minimum, bitcoin#17550,
we can remove the startup item code entirely, as the API we were using
was removed in macOS 10.12.

27d82b6 gui: remove macOS start on login code (fanquake)

Pull request description:

  The macOS startup item code was disabled for builds targeting macOS >
  `10.11` in #15208. Now that we require macOS `10.12` as a minimum (#17550),
  we can remove the startup item code entirely. The API we were using, `LSSharedFileListItemCopyResolvedURL`, `LSSharedFileListCopySnapshot` etc,
  was removed in macOS `10.12` SDK.

ACKs for top commit:
  jonasschnelli:
    utACK 27d82b6
  jonasschnelli:
    Tested ACK 27d82b6 - successfully compiled on 10.15.1

Tree-SHA512: 7420757b91c7820e6a63280887155394547134a9cebcf3721af0284da23292627f94cd431241e033075b3fd86d79ace3ebf1b25d17763acbf71e07a742395409

27d82b6 gui: remove macOS start on login code (fanquake)

Pull request description:

  The macOS startup item code was disabled for builds targeting macOS >
  `10.11` in bitcoin#15208. Now that we require macOS `10.12` as a minimum (bitcoin#17550),
  we can remove the startup item code entirely. The API we were using, `LSSharedFileListItemCopyResolvedURL`, `LSSharedFileListCopySnapshot` etc,
  was removed in macOS `10.12` SDK.

ACKs for top commit:
  jonasschnelli:
    utACK 27d82b6
  jonasschnelli:
    Tested ACK 27d82b6 - successfully compiled on 10.15.1

Tree-SHA512: 7420757b91c7820e6a63280887155394547134a9cebcf3721af0284da23292627f94cd431241e033075b3fd86d79ace3ebf1b25d17763acbf71e07a742395409

f9f210d doc: fix GetTimeMicros() comment in random.cpp (fanquake)
a889711 rand: remove getentropy() fallback for macOS < 10.12 (fanquake)

Pull request description:

  We [no longer support macOS < 10.12](#17550) (our binaries will not run), so remove the fallback for when `getentropy()` wasn't available. From the manpage:

  ```bash
  HISTORY
       The getentropy() function appeared in OSX 10.12
  ```

  Note that compiling on macOS you'll see a new unused function warning:
  ```bash
  random.cpp:256:13: warning: unused function 'GetDevURandom' [-Wunused-function]
  static void GetDevURandom(unsigned char *ent32)
              ^
  1 warning generated.
  ```

  This will likely be addressed as part of #17563.

ACKs for top commit:
  vasild:
    ACK f9f210d (code review, not tested)
  elichai:
    utACK f9f210d
  practicalswift:
    ACK f9f210d -- patch looks correct
  laanwj:
    ACK f9f210d
  hebasto:
    ACK f9f210d, tested on macOS 10.13.6: compiled

Tree-SHA512: 6bd2a721f23605a8bca0b7b51f42d628ebf92a18e74eb43194331ba745ee449223aff84119892781c40b188c70b75417447f4e390e3d9ac549292de2b1e8b308

… 10.12

f9f210d doc: fix GetTimeMicros() comment in random.cpp (fanquake)
a889711 rand: remove getentropy() fallback for macOS < 10.12 (fanquake)

Pull request description:

  We [no longer support macOS < 10.12](bitcoin#17550) (our binaries will not run), so remove the fallback for when `getentropy()` wasn't available. From the manpage:

  ```bash
  HISTORY
       The getentropy() function appeared in OSX 10.12
  ```

  Note that compiling on macOS you'll see a new unused function warning:
  ```bash
  random.cpp:256:13: warning: unused function 'GetDevURandom' [-Wunused-function]
  static void GetDevURandom(unsigned char *ent32)
              ^
  1 warning generated.
  ```

  This will likely be addressed as part of bitcoin#17563.

ACKs for top commit:
  vasild:
    ACK f9f210d (code review, not tested)
  elichai:
    utACK f9f210d
  practicalswift:
    ACK f9f210d -- patch looks correct
  laanwj:
    ACK f9f210d
  hebasto:
    ACK f9f210d, tested on macOS 10.13.6: compiled

Tree-SHA512: 6bd2a721f23605a8bca0b7b51f42d628ebf92a18e74eb43194331ba745ee449223aff84119892781c40b188c70b75417447f4e390e3d9ac549292de2b1e8b308

Summary:
```
Reasoning:

    10.10 has been unsupported since July 2017 (~3 years at v0.20.0
release)
    10.11 has been unsupported since July 2018 (~2 years at v0.20.0
release)
    macOS users are consistent at upgrading to new releases.
    Qt 5.12 LTS only supports macOS > 10.12. As long as we're supporting
macOS < 10.12 we would not be able to bump Qt in depends to 5.12 for the
v0.20.0 release.
```

Backport of core [[bitcoin/bitcoin#17550 | PR17550]].

Test Plan:
Run the OSX Gitian build.
Run the binary on 10.12 and 10.15.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5514

Summary:
```
Reasoning:

    10.10 has been unsupported since July 2017 (~3 years at v0.20.0
release)
    10.11 has been unsupported since July 2018 (~2 years at v0.20.0
release)
    macOS users are consistent at upgrading to new releases.
    Qt 5.12 LTS only supports macOS > 10.12. As long as we're supporting
macOS < 10.12 we would not be able to bump Qt in depends to 5.12 for the
v0.20.0 release.
```

Backport of core [[bitcoin/bitcoin#17550 | PR17550]].

Test Plan:
Run the OSX Gitian build.
Run the binary on 10.12 and 10.15.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5514

The macOS startup item code was disabled for builds targeting macOS >
10.11 in bitcoin#15208. Now that we require macOS 10.12 as a minimum, bitcoin#17550,
we can remove the startup item code entirely, as the API we were using
was removed in macOS 10.12.

Summary:
```
Reasoning:

    10.10 has been unsupported since July 2017 (~3 years at v0.20.0
release)
    10.11 has been unsupported since July 2018 (~2 years at v0.20.0
release)
    macOS users are consistent at upgrading to new releases.
    Qt 5.12 LTS only supports macOS > 10.12. As long as we're supporting
macOS < 10.12 we would not be able to bump Qt in depends to 5.12 for the
v0.20.0 release.
```

Backport of core [[bitcoin/bitcoin#17550 | PR17550]].
Includes fix D5530 (368a0fa) by Fabien.

Test Plan:
Run the OSX Gitian build.
Run the binary on 10.12 and 10.15.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5514

Modernise macOS cross-compilation toolchain

Cherry-picked from the following upstream PRs:

- bitcoin/bitcoin#13617
  - Excluding the QT GUI changes.
- bitcoin/bitcoin#17550
- bitcoin/bitcoin#16392
  - Excluding the QT GUI changes.
- bitcoin/bitcoin#18589
- bitcoin/bitcoin#19240
- bitcoin/bitcoin#19407
- bitcoin/bitcoin#17919
  - Only the ancillary changes, not the `FORCE_USE_SYSTEM_CLANG` change.
- bitcoin/bitcoin#19530

After these changes, macOS versions earlier than 10.12 are no longer supported.

To cross-compile for macOS:
- Follow the instructions in `contrib/macdeploy/README.md` to generate
  `Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers.tar.gz`
  (requires an Apple Developer Account)
- Extract it into `depends/SDKs` (creating that folder first if it does not exist)
- `HOST=x86_64-apple-darwin16 ./zcutil/build.sh`

Modernise macOS cross-compilation toolchain

Cherry-picked from the following upstream PRs:

- bitcoin/bitcoin#13617
  - Excluding the QT GUI changes.
- bitcoin/bitcoin#17550
- bitcoin/bitcoin#16392
  - Excluding the QT GUI changes.
- bitcoin/bitcoin#18589
- bitcoin/bitcoin#19240
- bitcoin/bitcoin#19407
- bitcoin/bitcoin#17919
  - Only the ancillary changes, not the `FORCE_USE_SYSTEM_CLANG` change.
- bitcoin/bitcoin#19530

After these changes, macOS versions earlier than 10.12 are no longer supported.

To cross-compile for macOS:
- Follow the instructions in `contrib/macdeploy/README.md` to generate
  `Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers.tar.gz`
  (requires an Apple Developer Account)
- Extract it into `depends/SDKs` (creating that folder first if it does not exist)
- `HOST=x86_64-apple-darwin16 ./zcutil/build.sh`

7d7bf2f build: set minimum supported macOS to 10.12 (fanquake)

Pull request description:

  Extracted from bitcoin#16392 as this doesn't need to wait for the other build changes.

  Reasoning:
  * `10.10` has been unsupported since July 2017 (~3 years at `v0.20.0` release)
  * `10.11` has been unsupported since July 2018  (~2 years at `v0.20.0` release)
  * macOS users are consistent at upgrading to new releases.
  * Qt 5.12 LTS only supports [macOS > 10.12](https://doc-snapshots.qt.io/qt5-5.12/supported-platforms.html). As long as we're supporting macOS < 10.12 we would not be able to bump Qt in depends to 5.12 for the `v0.20.0` release.

  Once we drop support for 10.12 and start using the 10.15 SDK there are some other follow ups:
  * Enabling support for [`thread_local`](https://github.com/bitcoin/bitcoin/blob/master/configure.ac#L901).
  * Removing some of the macOS notification code
  * Removing macOS [startup item code](https://github.com/bitcoin/bitcoin/blob/master/src/qt/guiutil.cpp#L695).

  There was also some related discussion in the `#bitcoin-builds` channel yesterday arvo.

ACKs for top commit:
  laanwj:
    ACK 7d7bf2f
  dongcarl:
    post-IRC-grilling-ACK 7d7bf2f

Tree-SHA512: 30b0ed75e3b4df2d3f94db2091b7982c1ea7be8fb3a2732d8efd1a53ef1e492d7265a47e90c38e92f66e638d10e9400a6ecb56e5093688bb26d1621645b453e8

27d82b6 gui: remove macOS start on login code (fanquake)

Pull request description:

  The macOS startup item code was disabled for builds targeting macOS >
  `10.11` in bitcoin#15208. Now that we require macOS `10.12` as a minimum (bitcoin#17550),
  we can remove the startup item code entirely. The API we were using, `LSSharedFileListItemCopyResolvedURL`, `LSSharedFileListCopySnapshot` etc,
  was removed in macOS `10.12` SDK.

ACKs for top commit:
  jonasschnelli:
    utACK 27d82b6
  jonasschnelli:
    Tested ACK 27d82b6 - successfully compiled on 10.15.1

Tree-SHA512: 7420757b91c7820e6a63280887155394547134a9cebcf3721af0284da23292627f94cd431241e033075b3fd86d79ace3ebf1b25d17763acbf71e07a742395409

… 10.12

f9f210d doc: fix GetTimeMicros() comment in random.cpp (fanquake)
a889711 rand: remove getentropy() fallback for macOS < 10.12 (fanquake)

Pull request description:

  We [no longer support macOS < 10.12](bitcoin#17550) (our binaries will not run), so remove the fallback for when `getentropy()` wasn't available. From the manpage:

  ```bash
  HISTORY
       The getentropy() function appeared in OSX 10.12
  ```

  Note that compiling on macOS you'll see a new unused function warning:
  ```bash
  random.cpp:256:13: warning: unused function 'GetDevURandom' [-Wunused-function]
  static void GetDevURandom(unsigned char *ent32)
              ^
  1 warning generated.
  ```

  This will likely be addressed as part of bitcoin#17563.

ACKs for top commit:
  vasild:
    ACK f9f210d (code review, not tested)
  elichai:
    utACK f9f210d
  practicalswift:
    ACK f9f210d -- patch looks correct
  laanwj:
    ACK f9f210d
  hebasto:
    ACK f9f210d, tested on macOS 10.13.6: compiled

Tree-SHA512: 6bd2a721f23605a8bca0b7b51f42d628ebf92a18e74eb43194331ba745ee449223aff84119892781c40b188c70b75417447f4e390e3d9ac549292de2b1e8b308

The macOS startup item code was disabled for builds targeting macOS >
10.11 in #15208. Now that we require macOS 10.12 as a minimum, #17550,
we can remove the startup item code entirely, as the API we were using
was removed in macOS 10.12.

e1b89ac Fix QPainter non-determinism on macOS (Andrew Chow)
831c317 macOS deploy: use the new plistlib API (Jonas Schnelli)
5857aaf doc: Document ALLOW_HOST_PACKAGES dependency option (skmcontrib)
2329e08 build: Fix behavior when ALLOW_HOST_PACKAGES unset (Hennadii Stepanov)
1768870 depends: native_ds_store 1.3.0 (fanquake)
3f9f3e5 depends: pull upstream libdmg-hfsplus changes (fanquake)
f7606dc depends: latest config.guess & config.sub (fanquake)
cc3ae74 depends: bump native_cctools for fixed lto with external clang (Cory Fields)
b26c648 depends: enable lto support for Apple's ld64 (Cory Fields)
50933d7 depends: Add documentation for FORCE_USE_SYSTEM_CLANG make flag (Carl Dong)
ba3ddf2 depends: Reformat make options as definition list (Carl Dong)
3b855a7 depends: Add justifications for macOS clang flags (Carl Dong)
4104de0 depends: specify libc++ header location for darwin (Cory Fields)
cd4335f depends: force a new host id string if FORCE_USE_SYSTEM_CLANG is in use (Cory Fields)
d30e1af depends: Allow building with system clang (Carl Dong)
234828b depends: Decouple toolchain + binutils (Carl Dong)
1dd3a5a doc: explain why passing -mlinker-version is required (fanquake)
5cc0d0f darwin: pass mlinker-version so that clang enables new features (Cory Fields)
813a552 macos: Bump to xcode 11.3.1 and 10.15 SDK (Cory Fields)
ee7085f depends: bump MacOS toolchain (Cory Fields)
e5b092b contrib: macdeploy: Remove historical extraction notes (Carl Dong)
5893caf contrib: macdeploy: Use apple-sdk-tools instead of xar+pbzx (Carl Dong)
9f2d4ba native_cctools: Don't use libc++ from pinned clang (Carl Dong)
0c8d217 Adapt rest of tooling to new SDK naming scheme (Carl Dong)
bdacfa8 contrib: macdeploy: Correctly generate macOS SDK (Carl Dong)
f7eee2c Fix naming of macOS SDK and clarify version (Andrew Chow)
62f9e23 build: use macOS 10.14 SDK (fanquake)
bc2e1af depends: native_cctools 921, ld64 409.12, libtapi 1000.10.8 (fanquake)
a296d87 depends: clang 6.0.1 (fanquake)
8f6c475 build: Set minimum supported macOS to 10.12 (Fuzzbawls)

Pull request description:

  This backports the following upstream PRs to update the macOS cross-compiling tools:

  bitcoin#17550
  bitcoin#16392
  bitcoin#18589
  bitcoin#19240
  bitcoin#19407
  bitcoin#17919
  bitcoin#19530
  bitcoin#17057
  bitcoin#20333
  bitcoin#18051
  bitcoin#19124
  bitcoin#20298
  bitcoin#20447

  The tools being updated are

  ### Clang
  Upgraded from `3.7.1` to `8.0.0`

  ### cctools

  * cctools `877.8` -> `949.0.1`
  * LD64 `253.9` -> `530`
  * TAPI `1000.10.8`

  ### DSStore
  Upgraded from `1.1.2` to `1.3.0` (this removes the biplist dependency)

  This also effectively bumps our minimum supported macOS version to 10.12 (Sierra).

ACKs for top commit:
  furszy:
    tested ACK e1b89ac
  random-zebra:
    utACK e1b89ac

Tree-SHA512: f5cec8db57e07d8855070646b9e1400d48aac1d01e3c2c3b3e134665c6372d6535f3328888bb9a75087f7b3d5231ecb4b509723bfa51bd40770ffe2810c67f65