This is meant to be a stop-gap until more robust tree building lands in
mozbuild. It simply proxies building through client.mk and captures
compiler warnings using the existing mechanism in mozbuild.
There are some DRY violations for how the compiler database is managed.
The more robust tree building code contains consolidated compiler
database logic. The DRY violations should disappear when that lands.
DONTBUILD (NPOTB)
