Define GLX_SAMPLE_BUFFERS_ARB and GLX_SAMPLES_ARB if they were not
defined by the OpenGL headers.

diff --git a/dlls/opengl32/opengl_ext.h b/dlls/opengl32/opengl_ext.h
index 90722e5..eaf9359 100644
--- a/dlls/opengl32/opengl_ext.h
+++ b/dlls/opengl32/opengl_ext.h
@@ -40,6 +40,14 @@
 #define WINAPI      __stdcall
 #define APIENTRY    WINAPI
 
+/* For compatibility with old Mesa headers */
+#ifndef GLX_SAMPLE_BUFFERS_ARB
+# define GLX_SAMPLE_BUFFERS_ARB             100000
+#endif
+#ifndef GLX_SAMPLES_ARB
+# define GLX_SAMPLES_ARB                    100001
+#endif
+
 /* X11 locking */
 
 extern void (*wine_tsx11_lock_ptr)(void);