GYP fixes: -Werror, snapshot.log, want_separate_host_toolset detection

tools/gyp/v8.gyp

 # 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 126 matching lines @@
          ['v8_compress_startup_data=="bz2"', {
             'defines': [
               'COMPRESS_STARTUP_DATA_BZ2',
             ],
           }],
         ],
         'configurations': {
           'Debug': {
             'defines': [
               'DEBUG',
-              '_DEBUG',
               'ENABLE_DISASSEMBLER',
               'V8_ENABLE_CHECKS',
               'OBJECT_PRINT',
             ],
             'msvs_settings': {
               'VCCLCompilerTool': {
                 'Optimization': '0',
 
                 'conditions': [
                   ['OS=="win" and component=="shared_library"', {
@@ skipping 207 matching lines @@
           'actions': [
             {
               'action_name': 'run_mksnapshot',
               'inputs': [
                 '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)mksnapshot<(EXECUTABLE_SUFFIX)',
               ],
               'outputs': [
                 '<(INTERMEDIATE_DIR)/snapshot.cc',
               ],
               'variables': {
-                'mksnapshot_flags': [],
+                'mksnapshot_flags': [
+                  '--log-snapshot-positions',
+                  '--logfile', '<(INTERMEDIATE_DIR)/snapshot.log',
+                ],
               },
               'conditions': [
                 ['v8_target_arch=="arm"', {
                   # The following rules should be consistent with chromium's
                   # common.gypi and V8's runtime rule to ensure they all generate
                   # the same correct machine code. The following issue is about
                   # V8's runtime rule about vfpv3 and neon:
                   # http://code.google.com/p/v8/issues/detail?id=914
                   'conditions': [
                     ['armv7==1', {
@@ skipping 718 matching lines @@
             }],
           ],
           'dependencies': [
             'v8'
           ],
         },
       ],
     }],
   ],
 }