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

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman requested changes to this pull request.

> This patch adds support for GCC bound member functions extension: https://gcc.gnu.org/onlinedocs/gcc/Bound-member-functions.html
> 
> Related issue: #22495 Closes #82727

I think this requires an RFC justifying carrying the extension. It's a non-conforming extension that we previously decided we would not implement (#22495 was closed as `WONTFIX`), and there's no real motivation for the feature request listed in #82727.

(Personally, I think #82727 should be closed as a duplicate of #22495 unless there's a very strong justification for carrying the extension.)

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