Replaced inline declarations with glext.h use.

tests/fsaa.c

@@ -30,14 +30,11 @@
 //========================================================================
 
 #include <GL/glfw3.h>
+#include <GL/glext.h>
 
 #include <stdio.h>
 #include <stdlib.h>
 
-#ifndef GL_ARB_multisample
-#define GL_MULTISAMPLE_ARB 0x809D
-#endif
-
 static void window_size_callback(GLFWwindow window, int width, int height)
 {
     glViewport(0, 0, width, height);