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

[Reid Kleckner via cfe-commits]

rnk wrote:

Seems reasonable to me, but I want @efriedma-quic  to approve as well, if this is a reasonable implementation of your direction.

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