The newly added dg-warning directive was missing the comment argument,
so the target selector was treated as comment and the warning was expected
on all targets when it should be expected only on llp64 targets.

2023-03-03  Jakub Jelinek  <jakub@redhat.com>

	PR testsuite/108991
	* gcc.dg/memchr-3.c: Add missing comment argument to dg-warning
	before target selector.