loader: try to raise SIGQUIT on timeout

so it's trivial to know in the showfailed summary what timedout.

tests/loader.c

@@ -176,6 +176,7 @@ static void test_cleaner(int sig)
 	kill(-child_gid, SIGQUIT);
 	waitpid(child_pid, &status, 0);
 	launch_gdb(test_name);
+	raise(SIGQUIT);
 	exit(EXIT_FAILURE);
 }