ARM64 support

[tristanlabelle]

Fix bad code generation issues and build hangs so that we can produce official ARM64 builds. This would unblock using Swift on Windows on Apple hardware via Parallels, which would be useful to macOS-based engineers at Apple and The Browser Company.

• Add cross-compile support to build.ps1
• Windows/ARM64 upstream swift CI/build up and running
• Fix the remaining ARM64 swift test failures

[tristanlabelle]

Some fixes thus far (in reverse chronological order):

• https://reviews.llvm.org/D155001
• Split a test for windows aarch64 and have it pass swiftlang/swift#68174
• Fix three tests for Windows AArch64 swiftlang/swift#67993
• Cherrypick the fix for the windows aarch64 relocation issue swiftlang/llvm-project#7276
• [AArch64][Windows] Fix the slot offset of the swift async context register. swiftlang/llvm-project#7107
• [AArch64][Windows] Fix the callee-saved registers for swiftcc on Windows/AArch64 swiftlang/llvm-project#7081

[hjyamauchi]

One more fix: llvm/llvm-project@0ecd884

[hjyamauchi]

llvm/llvm-project@f776e0b

[hjyamauchi]

swiftlang/swift#69836

[hjyamauchi]

swiftlang/swift#69929

[hjyamauchi]

swiftlang/swift#70050

[hjyamauchi]

swiftlang/swift#69935

[hjyamauchi]

swiftlang/swift#69368

[hjyamauchi]

swiftlang/swift#69375

[hjyamauchi]

swiftlang/swift#68780

[tristanlabelle]

@hjyamauchi , with your work we are able to build and run arm64 now. Should we complete this and file more granular follow-ups like fixing tests?

[hjyamauchi]

Sure

[tristanlabelle]

@hjyamauchi Ok, I'm completing this task because we do have arm64 support now. I don't know if the breakdown in the description is still valid but please file follow-up tasks as necessary.