firedrake: Moved to new overlay system and shared sub-scope

Firedrake contains a ton of inter-connected dependencies, many of
which are either firedrake specific or forked versions of upstream
packages.  Cleaner to create a firedrake sub-scope for all these.

pkgs/firedrake/parmetis.nix

@@ -0,0 +1,29 @@
+{ stdenv, fetchFromBitbucket, cmake
+, openmpi
+, metis }:
+
+stdenv.mkDerivation rec {
+  version = "4.0.3-p4";
+  name = "parmetis-${version}";
+
+  src = fetchFromBitbucket {
+    owner = "petsc";
+    repo = "pkg-parmetis";
+    rev = "v${version}";
+    sha256 = "088pzcyjgv1i8jbdznxnxy04cd8kk5y3a46vc7mh1na901s0msm2";
+  };
+
+  buildInputs = [
+    cmake
+    openmpi
+    metis
+  ];
+
+  cmakeFlags = [ "-DGKLIB_PATH=../headers" ];
+  makeFlags = [ "VERBOSE=1" ];
+
+  meta = with stdenv.lib; {
+    homepage = "http://glaros.dtc.umn.edu/gkhome/metis/parmetis";
+    description = "An MPI-based parallel library that implements a variety of algorithms for partitioning unstructured graphs, meshes, and for computing fill-reducing orderings of sparse matrices.";
+  };
+}