Fortran: allow RESTRICT qualifier also for optional arguments [PR100988]

Fortran: allow RESTRICT qualifier also for optional arguments [PR100988]

gcc/fortran/ChangeLog:

	PR fortran/100988
	* gfortran.h (IS_PROC_POINTER): New macro.
	* trans-types.cc (gfc_sym_type): Use macro in determination if the
	restrict qualifier can be used for a dummy variable.  Fix logic to
	allow the restrict qualifier also for optional arguments, and to
	not apply it to pointer or proc_pointer arguments.

gcc/testsuite/ChangeLog:

	PR fortran/100988
	* gfortran.dg/coarray_poly_6.f90: Adjust pattern.
	* gfortran.dg/coarray_poly_7.f90: Likewise.
	* gfortran.dg/coarray_poly_8.f90: Likewise.
	* gfortran.dg/missing_optional_dummy_6a.f90: Likewise.
	* gfortran.dg/pr100988.f90: New test.

Co-authored-by: Tobias Burnus  <tobias@codesourcery.com>