Add missing stdio.h include to wxGTK assert dialog code.

As we use FILE for saving the assert message to a file, we must include
<stdio.h> (which is not included from any other header, at least not under
Solaris).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69696 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/assertdlg_gtk.cpp

@@ -12,6 +12,8 @@
 #include "wx/gtk/assertdlg_gtk.h"
 #include "wx/gtk/private/gtk2-compat.h"
 
+#include <stdio.h>
+
 /* ----------------------------------------------------------------------------
    Constants
  ---------------------------------------------------------------------------- */