linux: fix compilation issue with recent Mesa (gentoo)

git-svn-id: http://pcsx2.googlecode.com/svn/trunk@5928 96395faa-99c1-11dd-bbfe-3dabce05a288

plugins/GSdx/GLLoader.h

@@ -22,6 +22,16 @@
 #pragma once
 
 #ifndef ENABLE_GLES
+// FIX compilation issue with Mesa 10
+// Note it might be possible to do better with the right include 
+// in the rigth order but I don't have time
+#ifndef APIENTRY
+#define APIENTRY
+#endif
+#ifndef APIENTRYP
+#define APIENTRYP APIENTRY *
+#endif
+
 // Allow compilation with older mesa
 
 #ifndef GL_ARB_copy_image