[Flang][OpenMP] Correct location information 1/n

This patch fixes location information of a few OpenMP constructs
and clauses. More fixes will come in follow-up patches.

This patch follows the same fixes for OpenACC (D131659).

Addresses some of the issues in https://github.com/llvm/llvm-project/issues/57215

Reviewed By: clementval

Differential Revision: https://reviews.llvm.org/D153887