expectk is only built when TK_BIN_DIR is defined.  the configure script
takes care of figuring out this value, but then they forgot to actually
write it out to the Makefile.

--- Makefile.in
+++ Makefile.in
@@ -24,6 +24,7 @@
 # SETUID = chmod u+s
 
 LIB_RUNTIME_DIR = $(DESTDIR)@libdir@
+TK_BIN_DIR = @TK_BIN_DIR@
 
 # The following Expect scripts are not necessary to have installed as
 # commands, but are very useful. Edit out what you don't want