mesa: Disable use of "pragma export" on OS X. clang doesn't understand it.

include/GL/osmesa.h

 /*
  * Mesa 3-D graphics library
  * Version:  6.5
  * 
  * Copyright (C) 1999-2005  Brian Paul   All Rights Reserved.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
  * to deal in the Software without restriction, including without limitation
  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
@@ skipping 83 matching lines @@
 #define OSMESA_HEIGHT           0x21
 #define OSMESA_FORMAT           0x22
 #define OSMESA_TYPE             0x23
 #define OSMESA_MAX_WIDTH        0x24  /* new in 4.0 */
 #define OSMESA_MAX_HEIGHT       0x25  /* new in 4.0 */
 
 
 typedef struct osmesa_context *OSMesaContext;
 
 
-#if defined(__QUICKDRAW__)
+/* See https://bugs.freedesktop.org/show_bug.cgi?id=77749 */
+#if 0 /* defined(__QUICKDRAW__) */
 #pragma export on
 #endif
 
 
 /*
  * Create an Off-Screen Mesa rendering context.  The only attribute needed is
  * an RGBA vs Color-Index mode flag.
  *
  * Input:  format - one of OSMESA_COLOR_INDEX, OSMESA_RGBA, OSMESA_BGRA,
  *                  OSMESA_ARGB, OSMESA_RGB, or OSMESA_BGR.
@@ skipping 159 matching lines @@
  */
 GLAPI void GLAPIENTRY
 OSMesaColorClamp(GLboolean enable);
 
 #ifdef __cplusplus
 }
 #endif
 
 
 #endif