[clang] [llvm] [win][aarch64] Always reserve frame pointers for Arm64 Windows (PR #146582)

[David Spickett via llvm-commits]

DavidSpickett wrote:

The actual error is the same as seen elsewhere:
```
$ /home/david.spickett/build-llvm-aarch64/bin/flang --target=aarch64-pc-windows-msvc -Werror ../llvm-project/flang/test/Semantics/windows.f90
flang-21: warning: unable to find a Visual Studio installation; try running Clang from a developer command prompt [-Wmsvc-not-found]
error: invalid value 'reserved' in '-mframe-pointer=reserved'
```
It was obscured by this test running the compiler via a Python script.

https://github.com/llvm/llvm-project/pull/146582