[Flang][openmp][openacc] Extend CheckNoBranching to handle branching provided by LabelEnforce.

`CheckNoBranching` is currently handling only illegal branching out for constructs
with `Parser::Name` in them.
Extend the same for handling illegal branching out caused by `Parser::Label` based statements.
This patch could possibly solve one of the issues(typically branching out) mentioned in D92735.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D93447