Add support for building the Dart VM for Android OS.

runtime/third_party/jscre/jscre.gypi

 # Copyright 2010 Google Inc. All Rights Reserved.
 
 {
   'targets': [
     {
       'target_name': 'libjscre',
       'type': 'static_library',
       'dependencies': [
       ],
       'include_dirs': [
         '.',
       ],
       'defines': [
         'SUPPORT_UTF8',
         'SUPPORT_UCP',
         'NO_RECURSE',
       ],
       'sources': [
         'ASCIICType.h',
         'config.h',
         'pcre.h',
         'pcre_internal.h',
         'ucpinternal.h',
         'pcre_compile.cpp',
         'pcre_exec.cpp',
         'pcre_tables.cpp',
         'pcre_ucp_searchfuncs.cpp',
         'pcre_xclass.cpp',
       ],
+      'conditions': [
+            ['dart_want_separate_host_toolset==1', {
+              'toolsets': ['host', 'target'],
+            }, {
+              'toolsets': ['target'],
+            }]
+      ],
     },
   ],
 }