MIPS: Implement sqrt in inline assembly.

Port r18506 (c7b2885)

Original commit message:
Call VSQRT directly to avoid the tiniest (1ulp) precision
error that occurs in the system-supplied sqrt on QNX/ARM.

All precision tests in SunSpider are now passing on this platform.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/131263003

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

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18523 ce2b1a6d-e550-0410-aec6-3dcde31c8c00