Implement truncated d-to-i as a stub on x86

- Added a general DoubleToIStub so that it's possible to extend to other platforms and non-truncating case.
- This version handles all cases of truncation (previous code deopted in some cases) and all source/destination register combinations without clobbering any temps.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/18612005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15645 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix LGapResolver::EmitMove for X64 when the dst is a double register and src is a constant

R=danno@chromium.org

Review URL: https://codereview.chromium.org/18301015

Patch from Haitao Feng <haitao.feng@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15646 ce2b1a6d-e550-0410-aec6-3dcde31c8c00