tests: Only run buffer-count test if we have at least mesa 10

https://bugs.freedesktop.org/show_bug.cgi?id=72835
diff --git a/tests/weston-test-client-helper.h b/tests/weston-test-client-helper.h
index c78fc28..6670ab3 100644
--- a/tests/weston-test-client-helper.h
+++ b/tests/weston-test-client-helper.h
@@ -124,4 +124,7 @@
 int
 get_n_egl_buffers(struct client *client);
 
+void
+skip(const char *fmt, ...);
+
 #endif