Update gl2.h and gl2ext.h headers from Khronos.

ppapi/native_client/src/shared/ppapi/nacl.scons

 # -*- python -*-
 # Copyright 2011 The Native Client Authors.  All rights reserved.
 # Use of this source code is governed by a BSD-style license that can
 # be found in the LICENSE file.
 
 import os
 import gyp_extract
 
 Import('env')
 
@@ skipping 21 matching lines @@
         ppapi_cpp_gypi, 'ppapi_cpp', '.*\.cc')
 )
 libppapi_cpp = env.NaClSdkLibrary('libppapi_cpp', cpp_sources)
 env.AddLibraryToSdk(libppapi_cpp)
 
 env.Append(CPPPATH=[
     '$SOURCE_ROOT/ppapi/lib/gl/gles2',
     '$SOURCE_ROOT/ppapi/lib/gl/include',
     ])
 
+env.Prepend(CPPDEFINES=['GL_GLEXT_PROTOTYPES'])
+
 # Load ppapi_gl.gypi
 ppapi_gl_gypi = gyp_extract.LoadGypFile(
     env.File('$SOURCE_ROOT/ppapi/ppapi_gl.gypi').abspath)
 
 # From ppapi_gl.gypi:ppapi_gles2:.*\.c
 gles2_sources = gyp_extract.GypTargetSources(
     ppapi_gl_gypi, 'ppapi_gles2', '.*\.c')
 libppapi_gles2 = env.NaClSdkLibrary('libppapi_gles2', gles2_sources)
 
 env.AddLibraryToSdk(libppapi_gles2)