Document current '-Wuninitialized'/'-Wmaybe-uninitialized' diagnostics for OpenACC...

Document current '-Wuninitialized'/'-Wmaybe-uninitialized' diagnostics for OpenACC test cases

... including "note: '[...]' was declared here" emitted since recent
commit 9695e1c23be5b5c55d572ced152897313ddb96ae
"Improve -Wuninitialized note location".

For those that seemed incorrect to me, I've placed XFAILed 'dg-bogus'es,
including one more instance of PR77504 etc., and several instances where
for "local variables" of reference-data-type reductions (etc.?) we emit
bogus (?) diagnostics.

For implicit data clauses (including 'firstprivate'), we seem to be missing
diagnostics, so I've placed XFAILed 'dg-warning's.

	gcc/testsuite/
	* c-c++-common/goacc/builtin-goacc-parlevel-id-size.c: Document
	current '-Wuninitialized' diagnostics.
	* c-c++-common/goacc/mdc-1.c: Likewise.
	* c-c++-common/goacc/nested-reductions-1-kernels.c: Likewise.
	* c-c++-common/goacc/nested-reductions-1-parallel.c: Likewise.
	* c-c++-common/goacc/nested-reductions-1-routine.c: Likewise.
	* c-c++-common/goacc/nested-reductions-2-kernels.c: Likewise.
	* c-c++-common/goacc/nested-reductions-2-parallel.c: Likewise.
	* c-c++-common/goacc/nested-reductions-2-routine.c: Likewise.
	* c-c++-common/goacc/uninit-dim-clause.c: Likewise.
	* c-c++-common/goacc/uninit-firstprivate-clause.c: Likewise.
	* c-c++-common/goacc/uninit-if-clause.c: Likewise.
	* gfortran.dg/goacc/array-with-dt-1.f90: Likewise.
	* gfortran.dg/goacc/array-with-dt-2.f90: Likewise.
	* gfortran.dg/goacc/array-with-dt-3.f90: Likewise.
	* gfortran.dg/goacc/array-with-dt-4.f90: Likewise.
	* gfortran.dg/goacc/array-with-dt-5.f90: Likewise.
	* gfortran.dg/goacc/derived-chartypes-1.f90: Likewise.
	* gfortran.dg/goacc/derived-chartypes-2.f90: Likewise.
	* gfortran.dg/goacc/derived-chartypes-3.f90: Likewise.
	* gfortran.dg/goacc/derived-chartypes-4.f90: Likewise.
	* gfortran.dg/goacc/derived-classtypes-1.f95: Likewise.
	* gfortran.dg/goacc/derived-types-2.f90: Likewise.
	* gfortran.dg/goacc/host_data-tree.f95: Likewise.
	* gfortran.dg/goacc/kernels-tree.f95: Likewise.
	* gfortran.dg/goacc/modules.f95: Likewise.
	* gfortran.dg/goacc/nested-reductions-1-kernels.f90: Likewise.
	* gfortran.dg/goacc/nested-reductions-1-parallel.f90: Likewise.
	* gfortran.dg/goacc/nested-reductions-1-routine.f90: Likewise.
	* gfortran.dg/goacc/nested-reductions-2-kernels.f90: Likewise.
	* gfortran.dg/goacc/nested-reductions-2-parallel.f90: Likewise.
	* gfortran.dg/goacc/nested-reductions-2-routine.f90: Likewise.
	* gfortran.dg/goacc/parallel-tree.f95: Likewise.
	* gfortran.dg/goacc/pr93464.f90: Likewise.
	* gfortran.dg/goacc/privatization-1-compute-loop.f90: Likewise.
	* gfortran.dg/goacc/privatization-1-compute.f90: Likewise.
	* gfortran.dg/goacc/privatization-1-routine_gang-loop.f90:
	Likewise.
	* gfortran.dg/goacc/privatization-1-routine_gang.f90: Likewise.
	* gfortran.dg/goacc/uninit-dim-clause.f95: Likewise.
	* gfortran.dg/goacc/uninit-firstprivate-clause.f95: Likewise.
	* gfortran.dg/goacc/uninit-if-clause.f95: Likewise.
	* gfortran.dg/goacc/uninit-use-device-clause.f95: Likewise.
	* gfortran.dg/goacc/wait.f90: Likewise.
	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/vred2d-128.c: Document
	current '-Wuninitialized' diagnostics.
	* testsuite/libgomp.oacc-fortran/data-5.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/gemm-2.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/gemm.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/optional-reduction.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/parallel-reduction.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/pr70643.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/pr96628-part1.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/privatized-ref-2.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/reduction-5.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/reduction-7.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/reference-reductions.f90:
	Likewise.