rustPlatform: forward fetchcargo args to stdenv

Most stdenv wrappers already work like this -- it allows greater
customisation.  We just have to be careful to remove arguments we're
using that shouldn't be passed to stdenv.  I've been conservative
here, because fetchcargo checksums shouldn't change lightly.

pkgs/build-support/rust/fetchcargo.nix

@@ -26,11 +26,11 @@ in
 , cargoUpdateHook ? ""
 , # whenever to also include the Cargo.lock in the output
   copyLockfile ? false
-}:
-stdenv.mkDerivation {
+, ...
+} @ args:
+stdenv.mkDerivation ({
   name = "${name}-vendor";
   nativeBuildInputs = [ cacert git cargo-vendor-normalise cargo ];
-  inherit src srcs patches sourceRoot;
 
   phases = "unpackPhase patchPhase installPhase";
 
@@ -76,4 +76,6 @@ stdenv.mkDerivation {
 
   impureEnvVars = stdenv.lib.fetchers.proxyImpureEnvVars;
   preferLocalBuild = true;
-}
+} // (builtins.removeAttrs args [
+  "name" "sha256" "cargoUpdateHook" "copyLockfile"
+]))