fix -Wunused-but-set-variable for gcc-4.6 on x64

SConstruct

 # Copyright 2011 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 380 matching lines @@
 CCTEST_EXTRA_FLAGS = {
   'all': {
     'CPPPATH': [join(root_dir, 'src')],
     'library:shared': {
       'CPPDEFINES': ['USING_V8_SHARED']
     },
   },
   'gcc': {
     'all': {
       'LIBPATH':      [abspath('.')],
-      'CCFLAGS':      ['$DIALECTFLAGS', '$WARNINGFLAGS'],
+      'CCFLAGS':      ['$DIALECTFLAGS', '$WARNINGFLAGS',
+                       '-Wno-unused-but-set-variable'],
       'CXXFLAGS':     ['-fno-rtti', '-fno-exceptions'],
       'LINKFLAGS':    ['$CCFLAGS'],
     },
     'os:linux': {
       'LIBS':         ['pthread'],
     },
     'os:macos': {
       'LIBS':         ['pthread'],
     },
     'os:freebsd': {
@@ skipping 1063 matching lines @@
 # version of scons.  Also, there's a bug in some revisions that
 # doesn't allow this flag to be set, so we swallow any exceptions.
 # Lovely.
 try:
   SetOption('warn', 'no-deprecated')
 except:
   pass
 
 
 Build()