[clang] [llvm] [Clang] Protect ObjCMethodList assignment operator against self-assignment (PR #97933)

[David Blaikie via cfe-commits]

dwblaikie wrote:

Is there existing test coverage (like, if you add an assertion, instead of an if/return - do any tests hit the assertion)? or could you add some?

https://github.com/llvm/llvm-project/pull/97933