MIPS: Avoid embedding x86 NaN constant in MacroAssembler code when snapshot is created.

BUG=
TEST=test262/15.4.4.15-8-b-ii-4
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/156803003

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19175 ce2b1a6d-e550-0410-aec6-3dcde31c8c00