FLAG_enable_testing_pragmas broken on *-precomp-win-*

[ghost]

It appears that at least one FLAG_.. is broken when running precompiled on Windows.

An easy way to replicate this is by removing the if(!FLAG_..) .. check in runtime/vm/native_api_impl.cc.
After which the following tests will fail:

• vmspecific_regress_37511_test
• vmspecific_regress_37511_callbacks_test
• vmspecific_function_gc_test
• vmspecific_function_callbacks_test

Importantly, removing the above line should not have any effect on these tests as they each explicitly set:
// VMOptions=--enable-testing-pragmas ...
Meaning the condition removed should always be a no-op.

It's quite possible this issue is related to #40579

[srawlins]

Tentatively triaging into area-vm

[ghost]

I have verified that linking against dart_precompiled_runtime.lib makes this issue go away:

sdk/runtime/bin/BUILD.gn

Lines 1050 to 1052 in 28c784d

	if (is_win) {
	# TODO(dartbug.com/40579): This wrongly links in dart.exe on precompiled.
	libs = [ "dart.lib" ]

I've noticed that dart_precompiled_runtime.exe will load the ffi_test_functions.dll and then load dart.exe, which leads me to believe that the flags are failing because they're loaded from the latter instead of dart_precompiled_runtime.exe.
The command line arguments are not passed to dart.exe when it is loaded.

So the root cause appears to be #40579.
In the short term I'm adding skips to the status files for *-precomp-win-*, and long term we should address #40579.

[ghost]

The specific issue here (and in #46061) has now been addressed, and any remaining work is related to #40579.