malloc: Run tests without calling mallopt [BZ #19469]

The compiled tests no longer refer to the mallopt symbol
from their main functions.  (Some tests still call mallopt
explicitly, which is fine.)

test-skeleton.c

@@ -346,8 +346,10 @@ main (int argc, char *argv[])
   unsigned int timeoutfactor = 1;
   pid_t termpid;
 
+#ifndef TEST_NO_MALLOPT
   /* Make uses of freed and uninitialized memory known.  */
   mallopt (M_PERTURB, 42);
+#endif
 
 #ifdef STDOUT_UNBUFFERED
   setbuf (stdout, NULL);