OpenMP: Integrate dynamic selectors with dispatch argument handling [PR118457]

OpenMP: Integrate dynamic selectors with dispatch argument handling [PR118457]

Support for dynamic selectors in "declare variant" was developed in
parallel with support for the adjust_args/append_args clauses and the
dispatch construct; they collided in a bad way.  This patch fixes the
"sorry" for calls that need both by removing the adjust_args/append_args
code from gimplify_call_expr and invoking it from the new variant
substitution code instead.  It's handled as a tree -> tree transformation
rather than tree -> gimple because eventually this code may end up being
invoked from the front ends instead of the gimplifier (see PR115076).

gcc/ChangeLog
	PR middle-end/118457
	* gimplify.cc (modify_call_for_omp_dispatch): New, containing
	code split from gimplify_call_expr and modified to emit tree
	instead of gimple.  Remove the error for falling through to a call
	to the base function.
	(expand_variant_call_expr): New, split from gimplify_variant_call_expr.
	Call modify_call_for_omp_dispatch on calls to
	variants in a dispatch construct context.
	(gimplify_variant_call_expr): Make it call expand_variant_call_expr
	to do the actual work.
	(gimplify_call_expr): Remove sorry for calls involving both
	dynamic/late selectors and adjust_args/append_args, and adjust
	for new interface.  Move adjust_args/append_args code to
	modify_call_for_omp_dispatch.
	(gimplify_omp_dispatch): Add some comments.

gcc/testsuite/ChangeLog
	PR middle-end/118457
	* c-c++-common/gomp/adjust-args-6.c: Remove xfails and adjust
	expected output.
	* c-c++-common/gomp/append-args-5.c: Adjust expected output.
	* c-c++-common/gomp/append-args-dynamic.c: New.
	* c-c++-common/gomp/dispatch-11.c: Adjust expected output.
	* gfortran.dg/gomp/dispatch-11.f90: Likewise.