If there is no libtermcap all the readline tests failed.

If there is no libtermcap all the readline tests failed.
This inappropriately disabled some capabilities which exist.

Now test for readline in -lreadline, if not found there, try it
in -ltermcap only if not in -lreadline.  If both libraries are
required, there will need to be more work, but I'm not sure
under what conditions both libraries would be required.