openmp, fortran: Add support for iterators in OpenMP 'target update' constructs ...

openmp, fortran: Add support for iterators in OpenMP 'target update' constructs (Fortran)

This adds Fortran support for iterators in 'to' and 'from' clauses in the
'target update' OpenMP directive.

gcc/fortran/

	* dump-parse-tree.cc (show_omp_namelist): Add iterator support for
	OMP_LIST_TO and OMP_LIST_FROM.
	* match.cc (gfc_free_namelist): Free namespace for OMP_LIST_TO and
	OMP_LIST_FROM.
	* openmp.cc (gfc_free_omp_clauses): Free namespace for OMP_LIST_TO
	and OMP_LIST_FROM.
	(gfc_match_motion_var_list): Parse 'iterator' modifier.
	(resolve_omp_clauses): Resolve iterators for OMP_LIST_TO and
	OMP_LIST_FROM.
	* trans-openmp.cc (gfc_trans_omp_clauses): Handle iterators in
	OMP_LIST_TO and OMP_LIST_FROM clauses.  Add expressions to
	iter_block rather than block.

gcc/testsuite/

	* gfortran.dg/gomp/target-update-iterators-1.f90: New.
	* gfortran.dg/gomp/target-update-iterators-2.f90: New.
	* gfortran.dg/gomp/target-update-iterators-3.f90: New.

libgomp/

	* testsuite/libgomp.fortran/target-update-iterators-1.f90: New.
	* testsuite/libgomp.fortran/target-update-iterators-2.f90: New.
	* testsuite/libgomp.fortran/target-update-iterators-3.f90: New.

Co-authored-by: Andrew Stubbs  <ams@baylibre.com>