X87: Check that external references are registered in the serializer.

port r22896

original commit message:
  Check that external references are registered in the serializer.
  Inspired by a patch by Slava Chigrin <vchigrin@yandex-team.ru>;

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/446003004

Patch from Chunyang Dai <chunyang.dai@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22952 ce2b1a6d-e550-0410-aec6-3dcde31c8c00