Since we want to have automated tests for our clang-based static analysis we first need to have the tree configured and for this the TC task that is created needs to be a a |build| task that uses the |mozharness|. Courtesy of gps this patch adds support for passing custom commands to |mach| inside the build context.

Comment on attachment 8967420 [details] Bug 1453709 - Add the possibility to run mach commands inside the build context. https://reviewboard.mozilla.org/r/236098/#review241852 Full disclosure: I initially authored this commit as part of another series. But sufficient time has passed that it has passed out of memory. This is a generic refactor and isn't doing anything terribly controversial. So I don't think there's a conflict with a soft self-review.

Pushed by bpostelnicu@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/d4997ce3e3ec Add the possibility to run mach commands inside the build context. r=gps