Fix build of matchbox-keyboard and matchbox-wm

These packages have buggy configure script. It adds -L/lib flag
for linker and thus wrong libraries are linked in.
Workaround this issue by setting expat=yes in configure
environment.

Signed-off-by: Darius Augulis <augulis.darius@gmail.com>
Signed-off-by: Paulius Zaleckas <paulius.zaleckas@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>