Description

Currently Linux builds override the default BUILD mode by putting it in
the generated config. That makes it sticky for manual runs of make,
which is inconsistent with how other platforms work.

Instead, pass the build mode as a command-line override, the same way
someone would if building directly with make. This makes the flow of
controlling the mode less confusing.

Minor incidental cleanup:

• Removes runInShell: true from the make call, as it's not needed, and running through the shell is generally more error-prone.
• Passes profile for Profile builds, rather than release. It currently won't build differently, but it's one less place that there's a hard-coded bypass of profile mode to clean up later.

Related Issues

Fixes #41528

Tests

I added the following tests: verify that release, profile, and debug all pass the correct override.

Also pulled some common test setup for the Linux build tests into helper functions.

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Breaking Change

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