space -> tab to fix symbol export on Cygwin

The patch looks useless at first sight, but the TAB is required to add
the symbol to libswipl.def, required to build libswipl.dll.  It would be
nice somehow, if the creation of the def file could be made whitespace-
agnostic.

Thanks,
Corinna
PORT: Fix Cygwin build machinery

Revert SOLIB for Cygwin to "lib", install into the arch specific lib and
bin subdirs.  In other words, install just as on any other UNIX system.
Drop the Cygwin-specific "cygpl.dll" name for the shared lib since it's
only used from within the SWI-Prolog installation dirs anyway.  This
allows to get rid of YA special case for Cygwin in configure.in, and it's
more in line with all other platforms.

With these changes, I can build a functional SWI-Prolog installation for
Cygwin which also correctly loads the package modules now (not a safe
bet before since I neglected to notice a build error with my patches
from last year).
Drop building unused swipl.def file. Don't install libswipl.def on Cygwin.

Get rid of building a local .def file on Cygwin which isn't used anyway.
Don't install the output def file at `make install' time on Cygwin since
it doesn't server any purpose on that platform.

This patch overrides the space->tab patch to SWI-Prolog.h which doesn't
have to be applied anymore.

Thanks,
Corinna
Updated xpce