OpenMP: Create additional interop objects with append_args.

OpenMP: Create additional interop objects with append_args.

This patch adds support for the case where #pragma omp declare variant
with append_args is used inside a #pragma omp dispatch interop that
specifies fewer interop args than required by the variant; new interop
objects are implicitly created and then destroyed around the call to the
variant, using the GOMP_interop builtin.

gcc/fortran/ChangeLog
	* trans-openmp.cc (gfc_trans_omp_declare_variant): Remove accidental
	redeclaration of pref.

gcc/ChangeLog
	* gimplify.cc (modify_call_for_omp_dispatch): Adjust arguments.
	Remove the "sorry" for the case where new interop objects must be
	constructed, and add code to make it work instead.
	(expand_variant_call_expr): Adjust arguments and call to
	modify_call_for_omp_dispatch.
	(gimplify_variant_call_expr): Simplify logic for calling
	expand_variant_call_expr.

gcc/testsuite/ChangeLog
	* c-c++-common/gomp/append-args-1.c: Adjust expected behavior.
	* c-c++-common/gomp/append-args-interop.c: New.
	* c-c++-common/gomp/dispatch-11.c: Adjust expected behavior.
	* g++.dg/gomp/append-args-1.C: Likewise.
	* gfortran.dg/gomp/append-args-interop.f90: New.
	* gfortran.dg/gomp/declare-variant-mod-2.f90: Adjust expected behavior.

libgomp/ChangeLog
	* libgomp.texi (OpenMP 5.1): Mark append_args as fully supported.

Co-Authored-By: Tobias Burnus <tburnus@baylibre.com>