Get third_party/libc++-static from Chromium via DEPS
Get third_party/libc++-static from Chromium via DEPS

The GN build rules for Mac use third_party/libc++-static to avoid
producing a runtime dependency on a system-installed libc++.  Get
this directory to the NaCl standalone GN build is more similar to
the Chromium GN build.

BUG= 545236
R=bradnelson@chromium.org, dschuff@chromium.org, ncbray@chromium.org

Review URL: https://codereview.chromium.org/1419793009

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client