Build gtest for both 'host' and 'target'.

The (future) relocation packing tool requires a host build of gtest for
its unit tests.

BUG=

Review URL: https://codereview.chromium.org/308913002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274251 0039d316-1c4b-4281-b951-d872f2087c98

testing/gtest.gyp

@@ -6,6 +6,7 @@
   'targets': [
     {
       'target_name': 'gtest',
+      'toolsets': ['host', 'target'],
       'type': 'static_library',
       'sources': [
         'gtest/include/gtest/gtest-death-test.h',