A64: Introduce a DeoptimizeIfMinusZero() helper.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/200413002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20010 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Don't generate keyed store ICs for global proxies.

BUG=352983
LOG=y
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/197873025

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20011 ce2b1a6d-e550-0410-aec6-3dcde31c8c00