Fix mpich cross compilation (disable fortran)

pkgs/mpich/default.nix

@@ -6,6 +6,12 @@
 , pmix
 , gfortran
 , symlinkJoin
+# Disabled when cross-compiling
+# To fix cross compilation, we should fill the values in:
+# https://github.com/pmodels/mpich/blob/main/maint/fcrosscompile/cross_values.txt.in
+# For each arch
+, enableFortran ? stdenv.hostPlatform == stdenv.buildPlatform
+, perl
 }:
 
 let
@@ -15,10 +21,13 @@ let
     paths = [ pmix.dev pmix.out ];
   };
 in mpich.overrideAttrs (old: {
-  buildInput = old.buildInputs ++ [
+  buildInputs = old.buildInputs ++ [
     libfabric
     pmixAll
   ];
+  nativeBuildInputs = old.nativeBuildInputs ++ [
+    perl
+  ];
   configureFlags = [
     "--enable-shared"
     "--enable-sharedlib"
@@ -31,7 +40,18 @@ in mpich.overrideAttrs (old: {
   ] ++ lib.optionals (lib.versionAtLeast gfortran.version "10") [
     "FFLAGS=-fallow-argument-mismatch" # https://github.com/pmodels/mpich/issues/4300
     "FCFLAGS=-fallow-argument-mismatch"
+  ] ++ lib.optionals (!enableFortran) [
+    "--disable-fortran"
   ];
+
+  preFixup = ''
+    # Ensure the default compilers are the ones mpich was built with
+    sed -i 's:CC="gcc":CC=${stdenv.cc}/bin/gcc:' $out/bin/mpicc
+    sed -i 's:CXX="g++":CXX=${stdenv.cc}/bin/g++:' $out/bin/mpicxx
+  '' + lib.optionalString enableFortran ''
+    sed -i 's:FC="gfortran":FC=${gfortran}/bin/gfortran:' $out/bin/mpifort
+  '';
+
   hardeningDisable = [ "all" ];
 
   meta = old.meta // {