Issue Description:

Hi Apple,

I've been trying to make a small change to the compiler on an M1 Mac and while the compiler build and runs but it is not possible to run tests !

Using the following command:
swift/utils/build-script --skip-build-benchmarks \
--skip-ios --skip-watchos --skip-tvos --swift-darwin-supported-archs "arm64" \
--sccache --release-debuginfo --test

I always get the following error:
– Configuring done
– Generating done
– Build files have been written to: /Users/johnholdsworth/swift-source/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64

• popd
  ~/swift-source
• /opt/homebrew/bin/cmake --build /Users/johnholdsworth/swift-source/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64 – -j8 all swift-test-stdlib-macosx-arm64
  ninja: error: 'stdlib/swift-test-stdlib-macosx-x86_64', needed by 'stdlib/CMakeFiles/swift-test-stdlib', missing and no known rule to make it
  ERROR: command terminated with a non-zero exit status 1, aborting

It is possible to edit the ninja.build manually to change stdlib/swift-test-stdlib-macosx-x86_64 to stdlib/swift-test-stdlib-macosx-arm64 and get things to work.

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1. Phony custom command for stdlib/CMakeFiles/swift-test-stdlib

build stdlib/CMakeFiles/swift-test-stdlib: phony stdlib/swift-test-stdlib-macosx-arm64

About 16 tests fail, mostly to do with the address sanitiser which looks like it needs a constant updated

ThreadSanitizer: unsupported vm address limit 0x800000000000, expected 0x000fc0000000.

I've looked at it but I don't speak cmake and while it feels like only a small change needs to be made somewhere, I've no idea where!