[clang] [Clang] Fix crash on malformed std::partial_ordering static members (PR #172001)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

@tbaederr @zwuis this looks good to me at this point, but as you've reviewed previously I'd just like to check if you have anything else to add?

https://github.com/llvm/llvm-project/pull/172001