nested-client: include platform.h

Missed because buliding nested clients requires cairo-glesv2.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

clients/nested-client.c

@@ -32,6 +32,8 @@
 #include <GLES2/gl2.h>
 #include <EGL/egl.h>
 
+#include "../shared/platform.h"
+
 struct window;
 struct seat;