[clang] [clang][Sema] close IsStandardConversion hole when adding cfi_unchecked_callee (PR #164592)

[Bruno De Fraine via cfe-commits]

brunodf-snps wrote:

Thanks for checking! I'll wait a day or two more to see if anyone else has remarks before merging this.

https://github.com/llvm/llvm-project/pull/164592