default-crate-overrides.nix: prevent git fetch

The build.rs script shipped with evdev-sys attempts to detect cross
compilation and uses a completely different codepath which does a
`git fetch` inside the build script.  This doesn't work in nixpkgs.

This PR adds a `touch libevdev/.git` to trick the `build.rs` into
thinking that it is not necessary to do a `git fetch`.

Thanks to @figsoda for finding this more-elegant solution to the
problem (my original solution needed to patch `build.rs`):

  NixOS#224893 (review)

Tested on:
- [x] `aarch64-linux` (cross from `x86_64-linux`)

pkgs/build-support/rust/default-crate-overrides.nix

@@ -36,6 +36,9 @@
 , alsa-lib
 , graphene
 , protobuf
+, autoconf
+, automake
+, libtool
 , ...
 }:
 
@@ -85,8 +88,16 @@ in
   };
 
   evdev-sys = attrs: {
-    nativeBuildInputs = [ pkg-config ];
+    nativeBuildInputs =
+      [ pkg-config
+        python3 autoconf automake libtool  # used only if HOST!=TARGET
+      ];
     buildInputs = [ libevdev ];
+
+    # This prevents libevdev's build.rs from trying to `git fetch` when HOST!=TARGET
+    prePatch = ''
+      touch libevdev/.git
+    '';
   };
 
   expat-sys = attrs: {