Added -Woverloaded-virtual to GCC flags, syncing scons and gyp builds.

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 278 matching lines @@
 }
 
 
 V8_EXTRA_FLAGS = {
   'gcc': {
     'all': {
       'WARNINGFLAGS': ['-Wall',
                        '-Werror',
                        '-W',
                        '-Wno-unused-parameter',
+                       '-Woverloaded-virtual',
                        '-Wnon-virtual-dtor']
     },
     'os:win32': {
       'WARNINGFLAGS': ['-pedantic', '-Wno-long-long']
     },
     'os:linux': {
       'WARNINGFLAGS': ['-pedantic'],
       'library:shared': {
         'soname:on': {
           'LINKFLAGS': ['-Wl,-soname,${SONAME}']
@@ skipping 1251 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()