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

Due to a different NaN representation on MIPS, the canonical nan
constant embedded in generated code that comes from snapshot will differ from
the one used on MIPS hardware.

TEST=mozilla/ecma/Array/15.4.4.2.js
BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/150663009

Patch from Dusan Milosavljevic <Dusan.Milosavljevic@rt-rk.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19118 ce2b1a6d-e550-0410-aec6-3dcde31c8c00