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/exodus.nix

@@ -0,0 +1,29 @@
+{ stdenv, fetchurl, cmake, gfortran
+, netcdf, hdf5 }:
+
+stdenv.mkDerivation rec {
+  version = "5.24";
+  name = "exodus-${version}";
+
+  src = fetchurl {
+    url = "http://ftp.mcs.anl.gov/pub/petsc/externalpackages/${name}.tar.bz2";
+    sha256 = "0pai6v322x1z09z4zp0plx5p9zg1g4645mpqh3kcfh93az070sn1";
+  };
+
+
+  buildInputs = [
+    gfortran
+    cmake
+    netcdf
+    hdf5
+  ];
+
+  patches = ./exodus-include.patch;
+  sourceRoot = "${name}/exodus";
+
+  meta = with stdenv.lib; {
+    homepage = "http://gsjaardema.github.io/seacas";
+    description = "A model developed to store and retrieve data for finite element analyses.";
+    license = licenses.bsd3;
+  };
+}