[clang-tools-extra] [clang-cl] Fix value of __FUNCTION__ and __FUNC__ in MSVC mode for c++. (PR #66120)

[Zahira Ammarguellat via cfe-commits]

zahiraam wrote:

> Hi @zahiraam - can we revert this change until [#66114 (comment)](https://github.com/llvm/llvm-project/issues/66114#issuecomment-1732319259) is resolved? Unfortunately this is impacting our downstream windows-x64 builder.

I have a fix for it. It should be ready by eod  (for me) today. But if that can't wait, sure we can revert it.

https://github.com/llvm/llvm-project/pull/66120