Fix build_overrides
Fix build_overrides

These variables were missing from the BUILDCONFIG, which means that for
the first import, the `current_os` would not be set.

R=c979aeeb7049b4ff5aca438de57bc9513f558ecc@chromium.org

Bug: 1139220
Change-Id: Ib964e7234ae38e3657139844951e2937225abd7a
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2656244
Auto-Submit: Tim van der Lippe <dba8716ee7f8d16236046f74d2167cb94410f6ed@chromium.org>
Commit-Queue: Liviu Rau <c979aeeb7049b4ff5aca438de57bc9513f558ecc@chromium.org>
Reviewed-by: Liviu Rau <c979aeeb7049b4ff5aca438de57bc9513f558ecc@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend