xf86Config: load DIX libraries before drivers on Cygwin

Cygwin doesn't have ELF rpath capabilities, so these libraries need
to be loaded before the drivers (namely dummy and nested) which
depend on their symbols.

Signed-off-by: Yaakov Selkowitz <yselkowitz@users.sourceforge.net>
Reviewed-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>