adding fix for arm64

[achicu]

Added code to handle ARM64 on Windows, similar to the code on llvm ARM64.

_ReadStatusReg(ARM64_CNTVCT) translates to mrs CNTVCT_EL0

https://github.com/llvm-mirror/clang/blob/master/test/CodeGen/arm64-microsoft-status-reg.cpp#L36

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[achicu]

@googlebot I signed it!

[janisozaur]

Duplicate of #1052

[achicu]

Looks like there's a fix now for this, closing my PR.