In C, it is a common pattern to have `static inline` functions in
headers to avoid ODR issues. Currently, when those headers are included
in a GMF, the names are not found when two-phase name lookup and ADL is
involved. Those names are removed by `Sema::AddOverloadCandidate`.
Similarly, in C++, sometimes people use templates with internal linkage
in headers.
As the GMF was designed to be a transitional mechanism for headers,
special case those functions in `Sema::AddOverloadCandidate`.
This fixes <https://github.com/llvm/llvm-project/issues/98021>.
