[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.

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