Build "snapshot_blob.bin" only for the host when using separate toolsets.

tools/gyp/v8.gyp

 # Copyright 2012 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 37 matching lines @@
           # dependency however the Android toolchain requires libv8_base.a
           # to appear before libv8_snapshot.a so it's listed explicitly.
           'dependencies': ['v8_base', 'v8_snapshot'],
         }],
         ['v8_use_snapshot!="true" and v8_use_external_startup_data==0', {
           # The dependency on v8_base should come from a transitive
           # dependency however the Android toolchain requires libv8_base.a
           # to appear before libv8_snapshot.a so it's listed explicitly.
           'dependencies': ['v8_base', 'v8_nosnapshot'],
         }],
-        ['v8_use_external_startup_data==1', {
+        ['v8_use_external_startup_data==1 and want_separate_host_toolset==0', {
           'dependencies': ['v8_base', 'v8_external_snapshot'],
         }],
+        ['v8_use_external_startup_data==1 and want_separate_host_toolset==1', {
+          'dependencies': ['v8_base', 'v8_external_snapshot#host'],
+        }],
         ['component=="shared_library"', {
           'type': '<(component)',
           'sources': [
             # Note: on non-Windows we still build this file so that gyp
             # has some sources to link into the component.
             '../../src/v8dll-main.cc',
           ],
           'include_dirs': [
             '../..',
           ],
@@ skipping 141 matching lines @@
             'V8_SHARED',
           ],
         }],
       ]
     },
     {
       'target_name': 'v8_external_snapshot',
       'type': 'static_library',
       'conditions': [
         ['want_separate_host_toolset==1', {
-          'toolsets': ['host', 'target'],
+          'toolsets': ['host'],
           'dependencies': [
             'mksnapshot#host',
             'js2c#host',
             'generate_trig_table#host',
             'natives_blob#host',
         ]}, {
           'toolsets': ['target'],
           'dependencies': [
             'mksnapshot',
             'js2c',
@@ skipping 1141 matching lines @@
         }],
         ['v8_compress_startup_data=="bz2"', {
           'libraries': [
             '-lbz2',
           ]
         }],
       ],
     },
   ],
 }