[compiler-rt] [win/asan] GetInstructionSize: Make `F6 C1 XX` a generic entry. (PR #118144)

[via llvm-commits]

bernhardu wrote:

> Would you like me to hit the "merge" button?

Thanks for reviewing, if there are no more concerns about the change, yes, please.

https://github.com/llvm/llvm-project/pull/118144