I don't intend to install ccache in the Debian build images. Hazard
builds are the only builds running on the desktop-build image still
using ccache somehow, and that gains them nothing, since the ccache
directory is not set to a cached directory on taskcluster, meaning
the build always starts with an empty cache. If anything, this currently
makes the build slower.
Eventually, those builds should be able to use sccache, once the
necessary setup moves out of mozconfig.cache.
Bug 1374940 adds a MOZ_TOOLCHAINS environment variable with a list of
path@task-id strings, where task-id is corresponding to the (possibly
optimized) toolchain job, and path corresponding to the
toolchain-artifact defined for that toolchain job.
We want to use that to pull artifacts instead of tooltool packages.
Hazard jobs use a specific tooltool-manifest field in their definition.
Since there is no post-processing happening on those definitions, and
since generalizing it would require adding the field to a bunch of
validation schemas, and the same code to various transforms, it's just
simpler to move to use environment variable definitions here too.
Eventually, tooltool manifests won't be necessary anyways, and those
environment variables will go away.
