feat(gs/keyboard): Integrate my layout with the depot

Integrate the keyboard layout for my Ergodox EZ, which is a layout for
QMK, with the depot, including exposing several cross-compilation
packages necessary to compile qmk for avr in third_party.

Change-Id: Idd43169a0a3cf0be2bd1a578fdaff70388a58bfc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/947
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

ci-builds.nix

@@ -101,5 +101,6 @@ in lib.fix (self: {
   glittershark = with depot.users.glittershark; [
     (systemFor system.system.chupacabra)
     xanthous
+    keyboard.layout
   ];
 })