emacs: handle three arguments correctly for genericBuild

Without this patch, if there are nativeBuildInputs,
propagatedUserEnvPkgs or postInstall in the arguments of genericBuild,
they will override the value set by genericBuild.  With this patch
applied, the argument and the value set by genericBuild are merged
instead.

pkgs/applications/editors/emacs/build-support/generic.nix

@@ -4,7 +4,8 @@
 
 let
   inherit (lib) optionalAttrs getLib;
-  handledArgs = [ "buildInputs" "packageRequires" "meta" ];
+  handledArgs = [ "buildInputs" "packageRequires" "propagatedUserEnvPkgs" "meta" ]
+    ++ lib.optionals (emacs.withNativeCompilation or false) [ "nativeBuildInputs" "postInstall" ];
 
   setupHook = writeText "setup-hook.sh" ''
     source ${./emacs-funcs.sh}
@@ -25,7 +26,10 @@ in
 { pname
 , version
 , buildInputs ? []
+, nativeBuildInputs ? []
 , packageRequires ? []
+, propagatedUserEnvPkgs ? []
+, postInstall ? ""
 , meta ? {}
 , ...
 }@args:
@@ -51,7 +55,7 @@ stdenv.mkDerivation (finalAttrs: ({
 
   buildInputs = [emacs texinfo] ++ packageRequires ++ buildInputs;
   propagatedBuildInputs = packageRequires;
-  propagatedUserEnvPkgs = packageRequires;
+  propagatedUserEnvPkgs = packageRequires ++ propagatedUserEnvPkgs;
 
   inherit setupHook;
 
@@ -69,7 +73,7 @@ stdenv.mkDerivation (finalAttrs: ({
 
   LIBRARY_PATH = "${getLib stdenv.cc.libc}/lib";
 
-  nativeBuildInputs = [ gcc ];
+  nativeBuildInputs = [ gcc ] ++ nativeBuildInputs;
 
   addEmacsNativeLoadPath = true;
 
@@ -84,7 +88,7 @@ stdenv.mkDerivation (finalAttrs: ({
     find $out/share/emacs -type f -name '*.el' -print0 \
       | xargs -0 -I {} -n 1 -P $NIX_BUILD_CORES sh -c \
           "emacs --batch --eval '(setq large-file-warning-threshold nil)' -f batch-native-compile {} || true"
-  '';
+  '' + postInstall;
 }
 
 // removeAttrs args handledArgs))