OpenACC: Pass pre-allocated 'ptrblock' to 'goacc_noncontig_array_create_ptrblock...

OpenACC: Pass pre-allocated 'ptrblock' to 'goacc_noncontig_array_create_ptrblock' [PR76739]

... to simplify later changes.  No functional change.

Follow-up for og12 commit 15d0f61a7fecdc8fd12857c40879ea3730f6d99f
"Merge non-contiguous array support patches".

	PR other/76739
	libgomp/
	* target.c (gomp_map_vars_internal): Pass pre-allocated 'ptrblock'
	to 'goacc_noncontig_array_create_ptrblock'.
	* oacc-parallel.c (goacc_noncontig_array_create_ptrblock): Adjust.
	* oacc-int.h (goacc_noncontig_array_create_ptrblock): Adjust.