Add compile-only win64 trybot.

BUG=353487
LOG=n
R=jochen@chromium.org
TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/385583004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22334 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

PRESUBMIT.py

@@ -176,5 +176,6 @@ def GetPreferredTryMasters(project, change):
       'v8_linux_layout_dbg': set(['defaulttests']),
       'v8_mac_rel': set(['defaulttests']),
       'v8_win_rel': set(['defaulttests']),
+      'v8_win64_rel': set(['defaulttests']),
     },
   }