[clang-tools-extra] [clang-cl] Fix for __FUNCTION__ in c++. (PR #66120)

[Zahira Ammarguellat via cfe-commits]

zahiraam wrote:

There are still some debug info LIT tests that are failing, but I am not going to edit them because I am not quite sure that's correct. Probably adding the "class" keyword shouldn't happen at all times even when the MSVCPolicy is true?

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