elisp-packages: fix AOT native-comp for several packages

Currently, AOT native-comp for emacs packages is implemented[1] in
postInstall. These packages override postInstall and do not keep
old.postInstall, so they do not do AOT native-comp. This patch fixes
this by keeping the old.postInstall in their overrides.

Note that I do not fix emacspeak because I have not found an elegant
way to do so.

[1]: a7cb8e36ac

pkgs/applications/editors/emacs/elisp-packages/elpa-packages.nix

@@ -96,7 +96,7 @@ self: let
           ./build.sh -j$NIX_BUILD_CORES
         '';
 
-        postInstall = ''
+        postInstall = (old.postInstall or "") + "\n" + ''
           ./install.sh --prefix=$out
         '';
 

pkgs/applications/editors/emacs/elisp-packages/melpa-packages.nix

@@ -186,7 +186,7 @@ let
             cd -
           '';
 
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             install -m=755 -D source/sqlite/emacsql-sqlite \
               $out/share/emacs/site-lisp/elpa/emacsql-sqlite-${old.version}/sqlite/emacsql-sqlite
           '';
@@ -301,7 +301,7 @@ let
             make
             popd
           '';
-          postInstall = ''
+          postInstall = (attrs.postInstall or "") + "\n" + ''
             outd=$(echo $out/share/emacs/site-lisp/elpa/libgit-**)
             mkdir $outd/build
             install -m444 -t $outd/build ./source/src/libegit2.so
@@ -426,7 +426,7 @@ let
             cd -
           '';
 
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             mkdir -p $out/bin
             install -m755 -Dt $out/bin ./source/server/telega-server
           '';
@@ -456,7 +456,7 @@ let
             pkgs.libtool
             (pkgs.zeromq.override { enableDrafts = true; })
           ];
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             mv $EZMQ_LIBDIR/emacs-zmq.* $out/share/emacs/site-lisp/elpa/zmq-*
             rm -r $out/share/emacs/site-lisp/elpa/zmq-*/src
             rm $out/share/emacs/site-lisp/elpa/zmq-*/Makefile
@@ -533,7 +533,7 @@ let
           ];
           # we need the proper out directory to exist, so we do this in the
           # postInstall instead of postBuild
-          postInstall = ''
+          postInstall = (old.postInstall or "") + "\n" + ''
             pushd source/build >/dev/null
             make
             install -m444 -t $out/share/emacs/site-lisp/elpa/vterm-** ../*.so