GCC generates instructions such as movdqa that requires 16-byte alignment.

R=ricow@chromium.org
BUG=v8:1505
TEST=

Review URL: http://codereview.chromium.org/7277031

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8432 ce2b1a6d-e550-0410-aec6-3dcde31c8c00