Fix for missing symbols on windows builds

indra/llrender/llgl.cpp

@@ -188,6 +188,9 @@ PFNGLWAITSYNCPROC				glWaitSync = NULL;
 PFNGLGETINTEGER64VPROC			glGetInteger64v = NULL;
 PFNGLGETSYNCIVPROC				glGetSynciv = NULL;
 
+// GL_APPLE_flush_buffer_range
+PFNGLBUFFERPARAMETERIAPPLEPROC	glBufferParameteriAPPLE = NULL;
+PFNGLFLUSHMAPPEDBUFFERRANGEAPPLEPROC glFlushMappedBufferRangeAPPLE = NULL;
 
 // vertex object prototypes
 PFNGLNEWOBJECTBUFFERATIPROC			glNewObjectBufferATI = NULL;