Don't use floating-point operations on Linux,x86 to compute strtod. Since the
floating-point stack on Linux is set to 80bit double rounding may occure.

When falling back to gay_strtod append several '0's so that Gay doesn't take
the same shortcut either.

BUG=
TEST=

Review URL: http://codereview.chromium.org/3851003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5650 ce2b1a6d-e550-0410-aec6-3dcde31c8c00