Add support for Windows on ARM

[jakepetroules]

No description provided.

[shahmishal]

@jakepetroules Can you look into the failure on arm before we merge this?

[jakepetroules]

• 6.1 looks nondeterministic, try re-running it for me
• nightly I'm not sure yet
• nightly-6.2 is due to http://download.swift.org/swift-6.2-branch/windows10-arm64/latest-build.json missing on the server (it's there for regular nightly)

[jakepetroules]

The Nov 3 arm64 snapshot is just broken and so the CI fails executing swift --version. Nothing we can do there except wait for a new toolchain build.

* thread #1, stop reason = Exception 0xc0000005 encountered at address 0x7ffe6fbecdf8: Access violation writing location 0x200000000
    frame #0: 0x00007ffe6fbecdf8 swiftCore.dll`_swift_pod_indirect_initializeBufferWithCopyOfBuffer + 408
swiftCore.dll`_swift_pod_indirect_initializeBufferWithCopyOfBuffer:
->  0x7ffe6fbecdf8 <+408>: str    x9, [x10]
    0x7ffe6fbecdfc <+412>: ldr    x30, [sp], #0x10
    0x7ffe6fbece00 <+416>: ret
    0x7ffe6fbece04 <+420>: str    x30, [sp, #-0x10]!
Target 0: (swift.exe) stopped.

[shahmishal]

nightly-6.2 is due to http://download.swift.org/swift-6.2-branch/windows10-arm64/latest-build.json missing on the server (it's there for regular nightly)

For now point to https://download.swift.org/swift-6.2-branch/windows10/latest-build.json