Fortran/OpenMP: cleanup gfc_free_omp_namelist

Fortran/OpenMP: cleanup gfc_free_omp_namelist

Move the logic to deduce what needs to be freed from the
caller to the callee by passing the OMP_LIST_... enum value
instead of multiple bool arguments to gfc_free_omp_namelist.

Additionally, add the name 'gfc_omp_list_type' to the existing
OMP_LIST_... enum values and OMP_LIST_NONE (== OMP_LIST_NUM)
as special value.

As an enum is available, use it properly and replace 0 by
OMP_LIST_FIRST in the list walks.

gcc/fortran/ChangeLog:

	* gfortran.h (enum gfc_omp_list_type): Add this name
	to the existing OMP_LIST... enum; add OMP_LIST_NONE.
	(gfc_free_omp_namelist): Take that enum as arg instead of bool args.
	* match.cc (gfc_free_omp_namelist): Update.
	* openmp.cc (gfc_free_omp_clauses, gfc_free_omp_declare_variant_list,
	gfc_match_omp_clause_reduction, gfc_match_omp_clauses,
	gfc_match_omp_allocate, gfc_match_omp_flush,
	gfc_match_omp_declare_target, resolve_omp_clauses,
	gfc_resolve_omp_parallel_blocks, resolve_omp_do,
	gfc_resolve_oacc_blocks, gfc_resolve_oacc_declare): Update
	gfc_free_omp_namelist call and used enum type instead of
	int.
	* st.cc (gfc_free_statement): Likewise.

Co-Authored-By: Julian Brown <julian@codesourcery.com>