Update //build, //buildtools, clang from chromium.
Update //build, //buildtools, clang from chromium.

This pulls in the latest GN binaries and config, and
also syncs up GYP.

We need to update things before we can land a GN fix
needed for ChromeOS.

R=bradnelson@chromium.org
BUG=621686

Review-Url: https://codereview.chromium.org/2115763002

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