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/fetchfossil/default.nix

@@ -0,0 +1,20 @@
+{stdenv, fossil, cacert}:
+
+{name ? null, url, rev, sha256}:
+
+stdenv.mkDerivation {
+  name = "fossil-archive" + (if name != null then "-${name}" else "");
+  builder = ./builder.sh;
+  nativeBuildInputs = [fossil cacert];
+
+  # Envvar docs are hard to find. A link for the future:
+  # https://www.fossil-scm.org/index.html/doc/trunk/www/env-opts.md
+  impureEnvVars = [ "http_proxy" ];
+
+  outputHashAlgo = "sha256";
+  outputHashMode = "recursive";
+  outputHash = sha256;
+
+  inherit url rev;
+  preferLocalBuild = true;
+}