Move mpich to pkgs/mpich

pkgs/mpich/default.nix

@@ -0,0 +1,39 @@
+{
+  mpich
+, pmix
+, libfabric
+, gfortran
+}:
+
+# Configure the OFI network for MPICH
+
+let
+  # pmix comes with the libraries in .out and headers in .dev
+  pmixAll = symlinkJoin {
+    name = "pmix-all";
+    paths = [ pmix.dev pmix.out ];
+  };
+in mpich.overrideAttrs (old: {
+  patches = (old.patches or []) ++ [
+    # See https://github.com/pmodels/mpich/issues/6946
+    ./mpich-fix-hwtopo.patch
+  ];
+  # Configure the network for MPICH
+  buildInput = old.buildInputs ++ [
+    libfabric
+    pmixAll
+  ];
+  configureFlags = [
+    "--enable-shared"
+    "--enable-sharedlib"
+    "--with-pm=no"
+    "--with-device=ch4:ofi"
+    "--with-pmi=pmix"
+    "--with-pmix=${pmixAll}"
+    "--with-libfabric=${libfabric}"
+    "--enable-g=log"
+  ] ++ lib.optionals (lib.versionAtLeast gfortran.version "10") [
+    "FFLAGS=-fallow-argument-mismatch" # https://github.com/pmodels/mpich/issues/4300
+    "FCFLAGS=-fallow-argument-mismatch"
+  ];
+});