X87: Rename ascii to one-byte where applicable.

port r23840.

original commit message:

  Rename ascii to one-byte where applicable.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/565853002

Patch from Jing Bao <jing.bao@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23895 ce2b1a6d-e550-0410-aec6-3dcde31c8c00