[OpenMP] libomp: add atomic functions for new OpenMP 5.1 atomics.

Added functions those implement "atomic compare".
Though clang does not use library interfaces to implement OpenMP atomics,
the functions added for consistency.
Also added missed functions for 80-bit floating min/max atomics.

Differential Revision: https://reviews.llvm.org/D110109

GitOrigin-RevId: 621d7a75b16dd2e00fe4acc6c1e2c33d91114d96
6 files changed