Fix compilation on arm64.

TBR=hpayer@chromium.org

Review URL: https://codereview.chromium.org/435413002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22866 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Precise sweeping makes zapping of garbage memory when trimming arrays obsolete

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/439863006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22867 ce2b1a6d-e550-0410-aec6-3dcde31c8c00