OpenACC: Improve implicit mapping for non-lexically nested offload regions

OpenACC: Improve implicit mapping for non-lexically nested offload regions

This patch enables use of the OMP_CLAUSE_RUNTIME_IMPLICIT_P flag for
OpenACC.

This allows code like this to work correctly:

  int arr[100];
  [...]
  #pragma acc enter data copyin(arr[20:10])

  /* No explicit mapping of 'arr' here.  */
  #pragma acc parallel
  { /* use of arr[20:10]... */ }

  #pragma acc exit data copyout(arr[20:10])

Otherwise, the implicit "copy" ("present_or_copy") on the parallel
corresponds to the whole array, and that fails at runtime when the
subarray is mapped.

The numbering of the GOMP_MAP_IMPLICIT bit clashes with the OpenACC
"non-contiguous" dynamic array support, so the GOMP_MAP_NONCONTIG_ARRAY_P
macro has been adjusted to account for that.

This behaviour relates to upstream OpenACC issue 490 (not yet resolved).

2023-06-16  Julian Brown  <julian@codesourcery.com>

gcc/
	* gimplify.cc (gimplify_adjust_omp_clauses_1): Set
	OMP_CLAUSE_MAP_RUNTIME_IMPLICIT_P for OpenACC also.

gcc/testsuite/
	* c-c++-common/goacc/combined-reduction.c: Adjust scan output.
	* c-c++-common/goacc/reduction-1.c: Likewise.
	* c-c++-common/goacc/reduction-2.c: Likewise.
	* c-c++-common/goacc/reduction-3.c: Likewise.
	* c-c++-common/goacc/reduction-4.c: Likewise.
	* c-c++-common/goacc/reduction-10.c: Likewise.
	* gfortran.dg/goacc/loop-tree-1.f90: Likewise.

include/
	* gomp-constants.h (GOMP_MAP_NONCONTIG_ARRAY_P): Tweak condition.

libgomp/
	* testsuite/libgomp.oacc-c-c++-common/implicit-mapping-1.c: New test.