[clang] [Clang] Add support for GCC bound member functions extension (PR #135649)

[Erich Keane via cfe-commits]

erichkeane wrote:

I too don't think this is an extension that we really want.  It is a pretty awful extension that does some pretty awful things to the language (and isn't implemented in a way that 'works right' in GCC anyway).  Unless there is a REALLY important workload that we absolutely need to compile, I'd prefer we don't.

https://github.com/llvm/llvm-project/pull/135649