[flang][OpenMP] Add one semantic check for data-sharing clauses

As OpenMP 5.0, for firstprivate, lastprivate, copyin, and copyprivate
clauses, if the list item is a polymorphic variable with the allocatable
attribute, the behavior is unspecified.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D127601