PoC: Cross-compilation support for custom toolchains #1129

Job	Run time
check-dead-code	36s
examples-darwin	2m 6s
examples-linux (alt-registry)	1m 0s
tests (https://releases.nixos.org/nix/nix-2.18.2/install)	1m 8s
examples-linux (build-std)	2m 12s
tests (https://releases.nixos.org/nix/nix-2.18.2/install, --override-input nixpkgs $(./ci/ref-fro...	1m 36s
examples-linux (cross-musl)	1m 16s
check-fmt	20s
examples-linux (cross-rust-overlay)	48s
examples-linux (cross-windows)	59s
examples-linux (custom-toolchain)	1m 17s
examples-linux (end-to-end-testing)	1m 8s
examples-linux (quick-start)	1m 30s
examples-linux (quick-start-simple)	1m 8s
examples-linux (quick-start-workspace)	2m 20s
examples-linux (sqlx)	1m 3s
examples-linux (trunk-workspace)	3m 3s
examples-linux (trunk)	1m 36s
all systems go	1s
	25m 7s

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