openmp: Refactor handling of iterators

openmp: Refactor handling of iterators

Move code to calculate the iteration size and to generate the iterator
expansion loop into separate functions.

Use OMP_ITERATOR_DECL_P to check for iterators in clause declarations.

gcc/c-family/

	* c-omp.cc (c_finish_omp_depobj): Use OMP_ITERATOR_DECL_P.

gcc/c/

	* c-typeck.cc (handle_omp_array_sections): Use OMP_ITERATOR_DECL_P.
	(c_finish_omp_clauses): Likewise.

gcc/cp/

	* pt.cc (tsubst_omp_clause_decl): Use OMP_ITERATOR_DECL_P.
	* semantics.cc (handle_omp_array_sections): Likewise.
	(finish_omp_clauses): Likewise.

gcc/

	* gimplify.cc (gimplify_omp_affinity): Use OMP_ITERATOR_DECL_P.
	(compute_omp_iterator_count): New.
	(build_omp_iterator_loop): New.
	(gimplify_omp_depend): Use OMP_ITERATOR_DECL_P,
	compute_omp_iterator_count and build_omp_iterator_loop.
	* tree-inline.cc (copy_tree_body_r): Use OMP_ITERATOR_DECL_P.
	* tree-pretty-print.cc (dump_omp_clause): Likewise.
	* tree.h (OMP_ITERATOR_DECL_P): New macro.