[clang] [llvm] [AArch64][COFF] Generate error when Branch-protection is used with A-key on Windows. (PR #203991)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

If this is the way forward, can it be made ready for review?

The 23.x branch is being branched in a couple of weeks, it would be great to have this sorted out before that.

https://github.com/llvm/llvm-project/pull/203991