loader: on timeout, rather terminate with SIGALRM

to avoid producing a core for loader, which we don't care about, that
overwrites the core for the test, which we do care about

tests/loader.c

@@ -176,7 +176,7 @@ static void test_cleaner(int sig)
 	kill(-child_gid, SIGQUIT);
 	waitpid(child_pid, &status, 0);
 	launch_gdb(test_name);
-	raise(SIGQUIT);
+	raise(SIGALRM);
 	exit(EXIT_FAILURE);
 }