At some point the propagation logic is being changed such that
nativeBuildInputs isn't included in buildInputs, which means that
pkg-config can't see anything in nativeBuildInputs.
The old method was having the alacritty build copy-pasted into the repo
and making minor changes. This worked but isn't really feasible as it
doesn't incoroprate upstream (build) changes without noticing.
This commit finally works out how to override buildRustPackage to set
the Cargo dependency.
