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

[Daniel Paoliello via cfe-commits]

dpaoliello wrote:

> Do we generate appropriate diagnostics for inline asm?

Good call, I'll have to look into that.

> Does the AArch64 backend actually support this flag? I briefly tried, and it looks like this doesn't actually do anything. I think we only implemented support for 32-bit Arm.

Ugh, I didn't realize that it didn't. I'll go take care of that.

> Should we make some corresponding change to LLVM so frontends that don't explicitly request some specific frame-pointer behavior follow the ABI by default?

That was going to be my next task.

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