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

[Zahira Ammarguellat via cfe-commits]

zahiraam wrote:

> @AaronBallman I removed the field that I added in the policy and tried to use the existing ones. That broke a few LIT tests but before fixing them I want to check with you if the combination of policy I have added in the unittest is correct. Thanks.

ping?

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