libgomp: call numa_available first when using libnuma

The documentation requires that numa_available() is called and only
when successful, other libnuma function may be called. Internally,
it does a syscall to get_mempolicy with flag=0 (which would return
the default policy if mode were not NULL). If this returns -1 (and
not 0) and errno == ENOSYS, the Linux kernel does not have the
get_mempolicy syscall function; if so, numa_available() returns -1
(otherwise: 0).

libgomp/

	PR libgomp/111024
	* allocator.c (gomp_init_libnuma): Call numa_available; if
	not available or not returning 0, disable libnuma usage.