the 20.03 branchoff happened months ago

`PYTRELLIS_LIBDIR` has been replaced by `TRELLIS_LIBDIR` in YosysHQ/nextpnr@1dc1164, which causes the build to fail on macOS.

In the current implementation, there's no possibility to modify the default
parameter for keepalive. This is a number that indicates how frequently
keepalive messages should be sent from the worker to the buildmaster,
expressed in seconds. The default (600) causes a message to be sent to
the buildmaster at least once every 10 minutes.

If the worker is behind a NAT box or stateful firewall, these messages
may help to keep the connection alive: some NAT boxes tend to forget about
a connection if it has not been used in a while. When this happens, the
buildmaster will think that the worker has disappeared, and builds will
time out. Meanwhile the worker will not realize than anything is wrong.

Signed-off-by: Sirio Balmelli <sirio@b-ad.ch>

Signed-off-by: Sirio Balmelli <sirio@b-ad.ch>

nixos/buildbot: enable configurable keepalive for buildbot worker

nextpnr: fix build on macOS

ChangeLog: https://github.com/racer-rust/racer/blob/v2.1.33/CHANGELOG.md#2132
Broken build: https://hydra.nixos.org/build/123837796

Please note that I intentionally didn't bump to `2.1.35` since it
requires nightly features. `2.1.33` is the latest version which supports
our current `rustc`-version (1.44.1) on nixpkgs `master`.

Closes #89481

yamllint: add top-level attribute

firefox/packages: drop old aliases

It's a dependency of pc-ble-driver-py, but it's no longer built
alongside it.

jabcode: init at git-2020-05-13