MIPS uses a different NAN bit pattern to represent quiet or
signalling NANs than does x86 or ARM.

BUG=
TEST=

Review URL: http://codereview.chromium.org/8510007
Patch from Gergely Kis <gergely@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9948 ce2b1a6d-e550-0410-aec6-3dcde31c8c00