[clang] -fsanitize=function: fix MSVC hashing to sugared type (PR #66816)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

@tru Would you agree to backport this fix to 17?

Strictly speaking there is an API change here, but I think it's a bit obscure and in any case, this change could catch misuse of it.

https://github.com/llvm/llvm-project/pull/66816