tests: Skip Xwayland test if binary isn't available

We know we're not going to succeed if the binary isn't installed, so
skip the test in that case.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

tests/xwayland-test.c

@@ -53,6 +53,9 @@ TEST(xwayland_client_test)
 	Atom atom, type_atom, actual_type;
 	char *wm_name;
 
+	if (access(XSERVER_PATH, X_OK) != 0)
+		exit(77);
+
 	display = XOpenDisplay(NULL);
 	if (!display)
 		exit(EXIT_FAILURE);