Enable double alignment for constructed arrays.

2nd (of 3) CL's to ensure complete alignment of FixedDoubleArrays.

TEST=
BUG=
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/35133002

Patch from Dusan Milosavljevic <Dusan.Milosavljevic@rt-rk.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17382 ce2b1a6d-e550-0410-aec6-3dcde31c8c00