[Clang][OpenMP] Refactor checking for mutually exclusive clauses. NFC.
Multiple clauses are mutually exclusive. This patch refactors the functions that check for pairs of mutually exclusive clauses into a generalized function which also also accepts a list of clause types if which at most one can appear.
NFC patch extracted out of D99459 by request.
Reviewed By: ABataev
Differential Revision: https://reviews.llvm.org/D103666