amtterm: allow compiling with gamt

This adds a graphical version of amtterm, called `gamt`, which
automatically gets built if gtk/gdk and vte are discovered.

It's gated behind a `withGamt` flag, defaulting to false, and available
as `gamt`.

This follows the same logic as qcam.

pkgs/by-name/am/amtterm/package.nix

@@ -3,10 +3,13 @@
   lib,
   stdenv,
   makeWrapper,
+  gtk3,
   openssl,
   perl,
   perlPackages,
   pkg-config,
+  vte,
+  withGamt ? false,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -18,7 +21,12 @@ stdenv.mkDerivation (finalAttrs: {
       perl
       SOAPLite
     ])
-    ++ [ openssl ];
+    ++ [ openssl ]
+
+    ++ lib.optionals withGamt [
+      gtk3
+      vte
+    ];
   nativeBuildInputs = [
     makeWrapper
     pkg-config

pkgs/top-level/all-packages.nix

@@ -8752,6 +8752,8 @@ with pkgs;
     protobuf = protobuf_21;
   };
 
+  gamt  = callPackage ../by-name/am/amtterm/package.nix { withGamt = true; };
+
   gcr = callPackage ../development/libraries/gcr { };
 
   gcr_4 = callPackage ../development/libraries/gcr/4.nix { };