[OpenMP][FIX] Introduce and use a simple generic-mode barrier

Before we had aligned barriers the `__kmpc_barrier_simple_spmd` was
OK to be used in the custom state machine. Now that SPMD barriers are
assumed to be aligned we need to use a "generic" barrier in places
that are not aligned.

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D112893