Darwin, testsuite: -bind_at_load is deprecated

gcc/testsuite/ChangeLog:

	* gcc.dg/darwin-ld-2.c: Ignore warning
	that -bind_at_load is deprecated.

gcc/testsuite/gcc.dg/darwin-ld-2.c

@@ -3,6 +3,7 @@
 
 /* { dg-options "-bind_at_load" } */
 /* { dg-do link { target *-*-darwin* } } */
+/* { dg-prune-output "-bind_at_load is deprecated" } */
 
 int main()
 {