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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

We have unit tests for these that live at: https://github.com/llvm/llvm-project/blob/32d16b64d3125e76f65d7d88a302a33618eb0e6e/clang/unittests/AST/TypePrinterTest.cpp and https://github.com/llvm/llvm-project/blob/32d16b64d3125e76f65d7d88a302a33618eb0e6e/clang/unittests/AST/DeclPrinterTest.cpp

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