I'm not sure this is the best place to post patches for expect, but we
seem to have other s.r.c-local changes similar to this, and I
understand we have expect only because it's used by dejagnu, and
dejagnu is regarded as part of gdb in s.r.c, so I'm only posting it
here.  The problem was that, on Cygwin, expect/configure couldn't find
the tk config file in the build tree because it wouldn't search tk/win
and tk/unix didn't exist, and expect/Dbgconfigure wouldn't even find
tcl/unix in the build tree, since it hadn't been updated after the
patch that added that code to aclocal.m4.  (Ab)using my powers of
configury maintainer (in the top level), I'm going ahead and checking
this in.  Please let me know in case I shouldn't do things like this
again.