Enable meta.cross for mpich related packages

pkgs/mpich/default.nix

@@ -45,10 +45,10 @@ in mpich.overrideAttrs (old: {
   ];
 
   preFixup = ''
-    sed -i "s:^CC=.*:CC=''${CC:-gcc}:" $out/bin/mpicc
-    sed -i "s:^CXX=.*:CXX=''${CXX:-g++}:" $out/bin/mpicxx
+    sed -i 's#^CC=.*#CC=''${CC:-gcc}#' $out/bin/mpicc
+    sed -i 's#^CXX=.*#CXX=''${CXX:-g++}#' $out/bin/mpicxx
   '' + lib.optionalString enableFortran ''
-    sed -i "s:^FC=.*:FC=''${FC:-gfortran}:" $out/bin/mpifort
+    sed -i 's#^FC=.*#FC=''${FC:-gfortran}#' $out/bin/mpifort
   '';
 
   hardeningDisable = [ "all" ];