CMake: move tricky code from CMake to Python

[gribozavr]

Removing an abstraction boundary also allowed me to fix a bug where we could not run long tests in optimized mode, which prevented us from being able to mark executable tests as long.

I tested this refactoring by running each check-swift-*-macosx-* target with --no-execute --show-unsupported arguments for lit, and inspected the output to make sure that we execute the right tests in each mode.

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[gribozavr]

@rintaro If you have time, could you review, please?

[gribozavr]

@swift-ci Please test

[gribozavr]

@swift-ci Please smoke test

[rintaro]

I feel I'm a little puzzled about test feature flags.
I'm pretty sure that I'm still not understanding completely,
but why not just add UNSUPPORTED: executable_test to existing long_test test cases?

[gribozavr]

but why not just add UNSUPPORTED: executable_test to existing long_test test cases?

I think doing so would disable them in, for example, check-swift-only_long-* configuration, which should run long executable tests in -Onone and long non-executable tests.

[rintaro]

nit: config.limit_to_features.discard("executable_test")

[gribozavr]

Thanks, fixed!

[rintaro]

but why not just add UNSUPPORTED: executable_test to existing long_test test cases?

I think doing so would disable them in, for example, check-swift-only_long-* configuration, which should run long executable tests in -Onone and long non-executable tests.

I see, thank you!

[gribozavr]

Thank you for the review!

@swift-ci Please smoke test and merge