[OpenMP] Restore backwards compatibility for libomptarget

The changes introduced in D87946 changed the API for libomptarget
functions. `__kmpc_push_target_tripcount` was a function in Clang 11.x
but was not given a backward-compatible interface. This change will
require people using Clang 13.x or 12.x to recompile their offloading

Reviewed By: jdoerfert cchen

Differential Revision: https://reviews.llvm.org/D98358

GitOrigin-RevId: 807466ef28125cf7268c860b09d5563c9c93602a
5 files changed