Make it possible to compile d8 for the host toolset as well

BUG=v8:1775
R=jkummerow@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/136763010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18618 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/d8.gyp

@@ -49,6 +49,11 @@
         'd8.cc',
       ],
       'conditions': [
+        [ 'want_separate_host_toolset==1', {
+          'toolsets': ['host', 'target'],
+        }, {
+          'toolsets': ['target'],
+        }],
         [ 'console=="readline"', {
           'libraries': [ '-lreadline', ],
           'sources': [ 'd8-readline.cc' ],