Clarify/verify OpenMP 'omp_calloc' zero-initialization for pinned memory

Clarify/verify OpenMP 'omp_calloc' zero-initialization for pinned memory

Clarification for og12 commit ab7520b3b4cd9fdabfd63652badde478955bd3b5
"libgomp: pinned memory".  No functional change.

	libgomp/
	* config/linux/allocator.c (linux_memspace_alloc)
	(linux_memspace_calloc): Clarify zero-initialization for pinned
	memory.
	* testsuite/libgomp.c/alloc-pinned-1.c: Verify zero-initialization
	for pinned memory.
	* testsuite/libgomp.c/alloc-pinned-2.c: Likewise.
	* testsuite/libgomp.c/alloc-pinned-3.c: Likewise.
	* testsuite/libgomp.c/alloc-pinned-4.c: Likewise.
	* testsuite/libgomp.c/alloc-pinned-5.c: Likewise.