Windows needed a few fixups to get the tests running:
1. bitcoin-tx needs a file extension in Windows. Take this opportunity to
   add an env file, which pulls variables out of our build config. This can
   be extended as needed, for now it's very simple.
2. After #1, split the args out of the exec key in the test data.
3. Correct the line-endings from windows stdout

c521b3ac6 Merge bitcoin#11: fixup define checks. Cleans up some oopses from #5.
8b1cd3753 fixup define checks. Cleans up some oopses from #5.
6b1508d6d Merge #6: Fixes typo
fceb80542 Merge bitcoin#10: Clean up compile-time warnings (gcc 7.1)
0ec2a343f Clean up compile-time warnings (gcc 7.1)
d4c268a35 Merge #5: Move helper functions out of sse4.2 object
8d4eb0847 Add HasAcceleratedCRC32C to port_win.h
77cfbfd25 crc32: move helper functions out of port_posix_sse.cc
4c1e9e016 silence compiler warnings about uninitialized variables
495316485 Merge #2: Prefer std::atomic over MemoryBarrier
2953978ef Fixes typo
f134284a1 Merge #1: Merge upstream LevelDB 1.20
ba8a445fd Prefer std::atomic over MemoryBarrier

git-subtree-dir: src/leveldb
git-subtree-split: c521b3ac654cfbe009c575eacf7e5a6e189bb5bb

…tion

d31e5c1 Fix shutdown in case of errors during initialization (Wladimir J. van der Laan)

Pull request description:

  PR bitcoin#10286 introduced a few steps which are not robust to early shutdown in initialization.

  Stumbled upon this with bitcoin#11781, not sure if there are other scenarios that can trigger it, but it's good to harden against this in any case.

  E.g.
  ```
  $ src/bitcoind  -debuglogfile=/dfdf
  Error: Could not open debug log file /dfdf
  Program received signal SIGSEGV, Segmentation fault.
  UnregisterValidationInterface (pwalletIn=0x0) at /.../bitcoin/src/validationinterface.cpp:82
  82          g_signals.m_internals->BlockChecked.disconnect(boost::bind(&CValidationInterface::BlockChecked, pwalletIn, _1, _2));
  (gdb) bt
  #0  UnregisterValidationInterface (pwalletIn=0x0) at /.../bitcoin/src/validationinterface.cpp:82
  #1  0x00005555555a11fc in Shutdown () at /.../bitcoin/src/init.cpp:196
  #2  0x00005555555961cc in AppInit (argc=<optimized out>, argv=<optimized out>) at /.../bitcoin/src/bitcoind.cpp:183
  #3  0x0000555555596249 in main (argc=0, argv=0x555555ecf200) at /.../bitcoin/src/bitcoind.cpp:19
  ```

Tree-SHA512: 7dd9570a9803514a17781bfadf1edde47e96df4e852cce2f423cab422e005fb94d44e777af1a6ea5167b04a4d889e848ae7a61a7e0e94232247ddea32ee70fc8