[clang] [clang] Fix nondeterminism in MemberPointerType (PR #137910)

[Maksim Ivanov via cfe-commits]

emaxx-google wrote:

> I'm still not sure I understand the problem this is solving, but I also don't see any harm in it, so I'm leaning towards accept here. Aaron can be the final approval though.

@AaronBallman I'd like to proceed with landing this as a short-term fix for the nondeterminism issue we're hitting at Google, but if you have any additional feedback I'm happy to address it in a follow-up. (We're also very interested in investigating the actual underlying issues that lead to these subtle problems, but it'll probably take much more time.)

https://github.com/llvm/llvm-project/pull/137910