Fix build with system ICU when using bundled v8.

build/linux/unbundle/icu.gyp

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'targets': [
     {
       'target_name': 'system_icu',
       'type': 'none',
+      'toolsets': ['host', 'target'],
       'direct_dependent_settings': {
         'defines': [
           'U_USING_ICU_NAMESPACE=0',
         ],
       },
       'link_settings': {
         'ldflags': [
           '<!@(icu-config --ldflags)',
         ],
         'libraries': [
           '<!@(icu-config --ldflags-libsonly)',
         ],
       },
     },
     {
       'target_name': 'icudata',
       'type': 'none',
       'dependencies': ['system_icu'],
       'export_dependent_settings': ['system_icu'],
     },
     {
       'target_name': 'icui18n',
       'type': 'none',
+      'toolsets': ['host', 'target'],
       'dependencies': ['system_icu'],
       'export_dependent_settings': ['system_icu'],
       'variables': {
         'headers_root_path': 'source/i18n',
         'header_filenames': [
           # This list can easily be updated using the command below:
           # find third_party/icu/source/i18n/unicode -iname '*.h' \
           # -printf "'%p',\n" | \
           # sed -e 's|third_party/icu/source/i18n/||' | sort -u
           'unicode/basictz.h',
@@ skipping 66 matching lines @@
           'unicode/vtzone.h',
         ],
       },
       'includes': [
         '../../build/shim_headers.gypi',
       ],
     },
     {
       'target_name': 'icuuc',
       'type': 'none',
+      'toolsets': ['host', 'target'],
       'dependencies': ['system_icu'],
       'export_dependent_settings': ['system_icu'],
       'variables': {
         'headers_root_path': 'source/common',
         'header_filenames': [
           # This list can easily be updated using the command below:
           # find third_party/icu/source/common/unicode -iname '*.h' \
           # -printf "'%p',\n" | \
           # sed -e 's|third_party/icu/source/common/||' | sort -u
           'unicode/brkiter.h',
@@ skipping 83 matching lines @@
           'unicode/uvernum.h',
           'unicode/uversion.h',
         ],
       },
       'includes': [
         '../../build/shim_headers.gypi',
       ],
     },
   ],
 }