Fix GL compile error on Mac OS X

panda/src/glstuff/glGraphicsStateGuardian_src.h

@@ -247,6 +247,7 @@ typedef void (APIENTRYP PFNGLVERTEXATTRIBL1UI64VPROC) (GLuint index, const GLuin
 typedef void (APIENTRYP PFNGLGETVERTEXATTRIBLUI64VPROC) (GLuint index, GLenum pname, GLuint64EXT *params);
 typedef void *(APIENTRYP PFNGLMAPBUFFERPROC) (GLenum target, GLenum access);
 typedef GLboolean (APIENTRYP PFNGLUNMAPBUFFERPROC) (GLenum target);
+typedef void (APIENTRYP PFNGLGETBUFFERSUBDATAPROC) (GLenum target, GLintptr offset, GLsizeiptr size, void *data);
 #endif  // OPENGLES
 #endif  // __EDG__