[clang] [clang-cl] Fix value of __FUNCTION__ in MSVC mode. (PR #67592)

[Zahira Ammarguellat via cfe-commits]

zahiraam wrote:

> > struct struct X
> 
> Interesting! The LIT test is passing on a debug build on Windows and generating the right output:
> 
> `VarDecl:{ResultType struct X}{TypedText f1} (50) (deprecated)`
> 
> I will try a release build.

It looks like I can reproduce it with the release build.

https://github.com/llvm/llvm-project/pull/67592