X87: Multiple stubs can point to the same calling convention

port r23546.

original commit message:
   Multiple stubs can point to the same calling convention

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/521223004

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

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23575 ce2b1a6d-e550-0410-aec6-3dcde31c8c00