x86/x64 port of Math.floor(x/y) to use integer division for specific divisor.

x86/x64 port of Math.floor(x/y) to use integer division for specific divisor.
Only handles when x is int32 and y is int32 constant.

BUG=v8:2038

Currently implemented by imul (not fpmul).
x86 and x64 algorithm differs a bit.
x86 implementation is kind of cumbersome, but I couldn't think of better ways.

Review URL: https://chromiumcodereview.appspot.com/10382033
Patch from Zheng Liu <zheng.z.liu@intel.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11887 ce2b1a6d-e550-0410-aec6-3dcde31c8c00