The mips related gyp variables and compiler flags for webview
and chromium builds are set externally. The CL ensures this
behaviour and prevents conflicts in configuration with standalone builds.

TEST=
BUG=
R=jkummerow@chromium.org, paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/707883002

Cr-Commit-Position: refs/heads/master@{#25243}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25243 ce2b1a6d-e550-0410-aec6-3dcde31c8c00