[og11] OpenMP/OpenACC: Move array_ref/indirect_ref handling code out of extract_base_...

[og11] OpenMP/OpenACC: Move array_ref/indirect_ref handling code out of extract_base_bit_offset

At Richard Biener's suggestion, this patch undoes the following patch:

  https://gcc.gnu.org/pipermail/gcc-patches/2021-June/571712.html

and moves the stripping of ARRAY_REFS/INDIRECT_REFS out of
extract_base_bit_offset and back into the (two) call sites of the
function. The difference between the two ways of looking through these
nodes comes down to (I think) what processing has been done on the
clause in question already: in the case where BASE_REF is non-NULL,
we are processing an OMP_CLAUSE_DECL for the first time. Conversely,
when BASE_REF is NULL, we are processing a node from the sorted list
that is being constructed after a GOMP_MAP_STRUCT node.

2021-06-07  Julian Brown  <julian@codesourcery.com>

gcc/
	* gimplify.cc (extract_base_bit_offset): Don't look through ARRAY_REFs or
	INDIRECT_REFs here.
	(build_struct_group): Reinstate previous behaviour for handling
	ARRAY_REFs/INDIRECT_REFs.