All calls to ftruncate() must have their return code checked.

Under FC11 rpm builds by default add the --fortify-source option which
ensures that functions flagged with certain attributes must have their
return codes checked.  Normally this is just a warning but we always
build with -Werror so this is fatal.  Simply wrap the function in a
verify call to ensure we catch a failure if there is one.

cmd/ztest/ztest.c

@@ -1161,7 +1161,7 @@ grow_vdev(vdev_t *vd, void *arg)
 		return (vd);
 
 	fsize = lseek(fd, 0, SEEK_END);
-	(void) ftruncate(fd, *newsize);
+	VERIFY(ftruncate(fd, *newsize) == 0);
 
 	if (zopt_verbose >= 6) {
 		(void) printf("%s grew from %lu to %lu bytes\n",