Merged r13617, r13622 into 3.15 branch.

Fix DoubleStackSlot-to-DoubleStackSlot moves on ia32. Unify platform-independent code.

Add regression test for r13617

BUG=173907,173907

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/12314149

git-svn-id: https://v8.googlecode.com/svn/branches/3.15@13742 ce2b1a6d-e550-0410-aec6-3dcde31c8c00