[clang] [clang] Fix constant evaluation of member pointer access into sibling class. (PR #150829)

[Timm Baeder via cfe-commits]

tbaederr wrote:

I fixed the worst offender in github.com/llvm/llvm-project/commit/193995d5a21dc8b923e19d9370aa8e1f374cd940, now `constant-expression-cxx2a.cpp` doesn't run into an infinite loop anymore and `constant-expression-cxx11.cpp` doesn't crash anymore.

https://github.com/llvm/llvm-project/pull/150829