[Flang][OpenMP][OpenACC] Fix exit out of a region in OpenMP parallel construct.

[Flang][OpenMP][OpenACC] Fix exit out of a region in OpenMP parallel construct.

From below mentioned standard references
OpenACC 3.0 Standards document
840 • A program may not branch into or out of an OpenACC parallel construct

OpenMP 5.0 Standards document
A program that branches into or out of a parallel region is non-conforming.

This patch
Resolves the issue of exit out of a parallel region, other branching out issues like goto statements are not handled with this patch.
Moves code from D87906 to be reused by other OpenMP/OpenACC to check-directive-structure.h.
Adds support in OpenMP parallel construct and a test case to verify.

Reviewed By: clementval

Differential Revision: https://reviews.llvm.org/D88655