emacs: Add jansson & harbuzz inputs

These are required for emacs 27 and above and the nix-community emacs
overlay are adding these via overrides.

Add these already on emacs 26 to be forwards compatible and require
less overrides in the overlay.

pkgs/applications/editors/emacs/default.nix

@@ -2,6 +2,7 @@
 , Xaw3d, libXcursor,  pkgconfig, gettext, libXft, dbus, libpng, libjpeg, libungif
 , libtiff, librsvg, gconf, libxml2, imagemagick, gnutls, libselinux
 , alsaLib, cairo, acl, gpm, AppKit, GSS, ImageIO, m17n_lib, libotf
+, jansson, harfbuzz
 , systemd ? null
 , withX ? !stdenv.isDarwin
 , withNS ? stdenv.isDarwin
@@ -62,6 +63,7 @@ stdenv.mkDerivation rec {
 
   buildInputs =
     [ ncurses gconf libxml2 gnutls alsaLib acl gpm gettext ]
+    [ ncurses gconf libxml2 gnutls alsaLib acl gpm gettext jansson harfbuzz.dev ]
     ++ lib.optionals stdenv.isLinux [ dbus libselinux systemd ]
     ++ lib.optionals withX
       [ xlibsWrapper libXaw Xaw3d libXpm libpng libjpeg libungif libtiff libXft