Test stdlib/test-bz22786 exits now with unsupported if malloc fails.

Test stdlib/test-bz22786 exits now with unsupported if malloc fails.

The test tries to allocate more than 2^31 bytes which will always fail on s390
as it has maximum 2^31bit of memory.
Before commit 6c3a8a9d868a8deddf0d6dcc785b6d120de90523, this test returned
unsupported if malloc fails.  This patch re enables this behaviour.

Furthermore support_delete_temp_files() failed to remove the temp directory
in this case as it is not empty due to the created symlink.
Thus the creation of the symlink is moved behind malloc.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
ChangeLog:

	* stdlib/test-bz22786.c (do_test): Return EXIT_UNSUPPORTED
	if malloc fails.