[clang] [llvm] [Clang] Add identifiers to retrieve the mangled name and the fully qualified name of functions (PR #145042)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

I think this should have an [RFC](https://llvm.org/docs/DeveloperPolicy.html#proposing-major-changes-rfcs) which explains what needs these extensions are solving. The fully-qualified name sounds like a use case for reflection, and neither macro seems to have a purpose in C (so are they only available in C++?). The current set of features exists only because the standard requires it or for compatibility with another compiler, but generally are only used as a debugging or logging aid, so it's not clear why we'd need to add two more.

https://github.com/llvm/llvm-project/pull/145042