openmp: Add alloc_align attribute to omp_aligned_*alloc and testcase for omp_realloc

openmp: Add alloc_align attribute to omp_aligned_*alloc and testcase for omp_realloc

This patch adds alloc_align attribute to omp_aligned_{,c}alloc so that if
the first argument is constant, GCC can assume requested alignment.

Additionally, it adds testsuite coverage for omp_realloc which I haven't
managed to write in the patch from yesterday.

2021-10-01  Jakub Jelinek  <jakub@redhat.com>

	* omp.h.in (omp_aligned_alloc, omp_aligned_calloc): Add
	__alloc_align__ (1) attribute.
	* testsuite/libgomp.c-c++-common/alloc-9.c: New test.