tcl: enable threads and 64-bit support

64-bit support is only enabled on 64-bit systems

pkgs/development/interpreters/tcl/generic.nix

@@ -19,13 +19,14 @@ stdenv.mkDerivation rec {
   '';
 
   configureFlags = [
+    "--enable-threads"
     # Note: using $out instead of $man to prevent a runtime dependency on $man.
     "--mandir=${placeholder "out"}/share/man"
     "--enable-man-symlinks"
     # Don't install tzdata because NixOS already has a more up-to-date copy.
     "--with-tzdata=no"
     "tcl_cv_strtod_unbroken=ok"
-  ];
+  ] ++ stdenv.lib.optional stdenv.is64bit "--enable-64bit";
 
   enableParallelBuilding = true;