Add '-Wopenacc-parallelism'

Add '-Wopenacc-parallelism'

... to diagnose potentially suboptimal choices regarding OpenACC parallelism.

Not enabled by default: too noisy ("*potentially* suboptimal choices"); see
XFAILed 'dg-bogus'es.

	gcc/c-family/
	* c.opt (Wopenacc-parallelism): New.
	gcc/fortran/
	* lang.opt (Wopenacc-parallelism): New.
	gcc/
	* omp-offload.c (oacc_validate_dims): Implement
	'-Wopenacc-parallelism'.
	* doc/invoke.texi (-Wopenacc-parallelism): Document.
	gcc/testsuite/
	* c-c++-common/goacc/diag-parallelism-1.c: New.
	* c-c++-common/goacc/acc-icf.c: Specify '-Wopenacc-parallelism',
	and match diagnostics, as appropriate.
	* c-c++-common/goacc/classify-kernels-unparallelized.c: Likewise.
	* c-c++-common/goacc/classify-kernels.c: Likewise.
	* c-c++-common/goacc/classify-parallel.c: Likewise.
	* c-c++-common/goacc/classify-routine.c: Likewise.
	* c-c++-common/goacc/classify-serial.c: Likewise.
	* c-c++-common/goacc/kernels-decompose-1.c: Likewise.
	* c-c++-common/goacc/kernels-decompose-2.c: Likewise.
	* c-c++-common/goacc/parallel-dims-1.c: Likewise.
	* c-c++-common/goacc/parallel-reduction.c: Likewise.
	* c-c++-common/goacc/pr70688.c: Likewise.
	* c-c++-common/goacc/routine-1.c: Likewise.
	* c-c++-common/goacc/routine-level-of-parallelism-2.c: Likewise.
	* c-c++-common/goacc/uninit-dim-clause.c: Likewise.
	* gfortran.dg/goacc/classify-kernels-unparallelized.f95: Likewise.
	* gfortran.dg/goacc/classify-kernels.f95: Likewise.
	* gfortran.dg/goacc/classify-parallel.f95: Likewise.
	* gfortran.dg/goacc/classify-routine.f95: Likewise.
	* gfortran.dg/goacc/classify-serial.f95: Likewise.
	* gfortran.dg/goacc/kernels-decompose-1.f95: Likewise.
	* gfortran.dg/goacc/kernels-decompose-2.f95: Likewise.
	* gfortran.dg/goacc/parallel-tree.f95: Likewise.
	* gfortran.dg/goacc/routine-4.f90: Likewise.
	* gfortran.dg/goacc/routine-level-of-parallelism-1.f90: Likewise.
	* gfortran.dg/goacc/routine-module-mod-1.f90: Likewise.
	* gfortran.dg/goacc/routine-multiple-directives-1.f90: Likewise.
	* gfortran.dg/goacc/uninit-dim-clause.f95: Likewise.
	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/firstprivate-1.c: Specify
	'-Wopenacc-parallelism', and match diagnostics, as appropriate.
	* testsuite/libgomp.oacc-c-c++-common/loop-auto-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-w-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-w-2.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-w-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/mode-transitions.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/par-reduction-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/par-reduction-2.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/parallel-dims.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/parallel-reduction.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/pr85381-3.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/private-variables.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/reduction-5.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/reduction-7.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/routine-g-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/routine-w-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/routine-wv-2.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/static-variable-1.c:
	Likewise.
	* testsuite/libgomp.oacc-fortran/optional-private.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/par-reduction-2-1.f: Likewise.
	* testsuite/libgomp.oacc-fortran/par-reduction-2-2.f: Likewise.
	* testsuite/libgomp.oacc-fortran/parallel-dims.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/parallel-reduction.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/pr84028.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/private-variables.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/reduction-1.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/reduction-5.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/reduction-6.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/routine-7.f90: Likewise.

Co-Authored-By: Nathan Sidwell <nathan@codesourcery.com>
Co-Authored-By: Tom de Vries <vries@codesourcery.com>
Co-Authored-By: Julian Brown <julian@codesourcery.com>
Co-Authored-By: Kwok Cheung Yeung <kcy@codesourcery.com>