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/development/tools/build-managers/ekam/default.nix

@@ -0,0 +1,67 @@
+{ lib, stdenv, fetchFromGitHub, capnproto }:
+
+stdenv.mkDerivation {
+  pname = "ekam";
+  version = "unstable-2021-09-18";
+
+  src = fetchFromGitHub {
+    owner = "capnproto";
+    repo = "ekam";
+    rev = "77c338f8bd8f4a2ce1e6199b2a52363f1fccf388";
+    sha256 = "0q4bizlb1ykzdp4ca0kld6xm5ml9q866xrj3ijffcnyiyqr51qr8";
+  };
+
+  # The capnproto *source* is required to build ekam.
+  # https://github.com/capnproto/ekam/issues/5
+  #
+  # Specifically, the git version of the source is required, as
+  # capnproto release tarballs do not include ekam rule files.
+  postUnpack = ''
+    mkdir -p $sourceRoot/deps
+    cp -r ${capnproto.src} $sourceRoot/deps/capnproto
+  '';
+
+  postPatch = ''
+    # A single capnproto test file expects to be able to write to
+    # /var/tmp.  We change it to use /tmp because /var is not available
+    # under nix-build.
+    substituteInPlace deps/capnproto/c++/src/kj/filesystem-disk-test.c++ \
+      --replace "/var/tmp" "/tmp"
+  '';
+
+  # NIX_ENFORCE_PURITY prevents ld from linking against anything outside
+  # of the nix store -- but ekam builds capnp locally and links against it,
+  # so that causes the build to fail. So, we turn this off.
+  #
+  # See: https://nixos.wiki/wiki/Development_environment_with_nix-shell#Troubleshooting
+  preBuild = ''
+    unset NIX_ENFORCE_PURITY
+  '';
+
+  makeFlags = [
+    "PARALLEL=$(NIX_BUILD_CORES)"
+  ];
+
+  installPhase = ''
+    mkdir $out
+    cp -r bin $out
+
+    # Remove capnproto tools; there's a separate nix package for that.
+    rm $out/bin/capnp*
+    # Don't distribute ekam-bootstrap, which is not needed outside this build.
+    rm $out/bin/ekam-bootstrap
+  '';
+
+  meta = with lib; {
+    description = ''Build system ("make" in reverse)'';
+    longDescription = ''
+      Ekam ("make" spelled backwards) is a build system which automatically
+      figures out what to build and how to build it purely based on the
+      source code. No separate "makefile" is needed.
+    '';
+    homepage = "https://github.com/capnproto/ekam";
+    license = licenses.asl20;
+    platforms = platforms.linux;
+    maintainers = [ maintainers.garrison ];
+  };
+}