uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

pkgs/build-support/rust/sysroot/src.nix

@@ -0,0 +1,26 @@
+{ lib, stdenv, rustPlatform, buildPackages
+, originalCargoToml ? null
+}:
+
+stdenv.mkDerivation {
+  name = "cargo-src";
+  preferLocalBuild = true;
+
+  unpackPhase = "true";
+  dontConfigure = true;
+  dontBuild = true;
+
+  installPhase = ''
+    export RUSTC_SRC=${rustPlatform.rustLibSrc.override { }}
+  ''
+  + lib.optionalString (originalCargoToml != null) ''
+    export ORIG_CARGO=${originalCargoToml}
+  ''
+  + ''
+    ${buildPackages.python3.withPackages (ps: with ps; [ toml ])}/bin/python3 ${./cargo.py}
+    mkdir -p $out/src
+    touch $out/src/lib.rs
+    cp Cargo.toml $out/Cargo.toml
+    cp ${./Cargo.lock} $out/Cargo.lock
+  '';
+}