OpenMP/Fortran: Add support for OpenMP 5.2 linear clause syntax

OpenMP/Fortran: Add support for OpenMP 5.2 linear clause syntax

Fortran part to C/C++
commit r13-1002-g03b71406323ddc065b1d7837d8b43b17e4b048b5

gcc/fortran/ChangeLog:

	* gfortran.h (gfc_omp_namelist): Update by creating 'linear' struct,
	move 'linear_op' as 'op' to id and add 'old_modifier' to it.
	* dump-parse-tree.cc (show_omp_namelist): Update accordingly.
	* module.cc (mio_omp_declare_simd): Likewise.
	* trans-openmp.cc (gfc_trans_omp_clauses): Likewise.
	* openmp.cc (resolve_omp_clauses): Likewise; accept new-style
	'val' modifier with do/simd.
	(gfc_match_omp_clauses): Handle OpenMP 5.2 linear clause syntax.

libgomp/ChangeLog:

	* libgomp.texi (OpenMP 5.2): Mark linear-clause change as 'Y'.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/linear-4.c: New test.
	* gfortran.dg/gomp/linear-2.f90: New test.
	* gfortran.dg/gomp/linear-3.f90: New test.
	* gfortran.dg/gomp/linear-4.f90: New test.
	* gfortran.dg/gomp/linear-5.f90: New test.
	* gfortran.dg/gomp/linear-6.f90: New test.
	* gfortran.dg/gomp/linear-7.f90: New test.
	* gfortran.dg/gomp/linear-8.f90: New test.

Co-authored-by: Jakub Jelinek <jakub@redhat.com>