Restore abilty to compile without Tk

Patch made against cvs version 5.44.1.13 allowing to compile again without Tk
When expect is only intented to run gcc test, that make no sense to require Tk installed.

I have not restored --with-x=no but changed existing --with-tk to support variant --with-tk=no.
If that's desirable, I could rework my patch to use again --with-x=no.

I have not changed the indentation despite having added one if fi level in 3 m4 macro.
That make the patch much smaller and more readable. I could update the indentation at maintainer request.