With -current sources, I don't see the first build problem -- for
me prop_array.c and the other libprop objects build just fine in
the i386/stand tree.  The .d file for prop_array.c indicates that
it picks up prop_array.h from $DESTDIR/usr/include/prop/.

As for the second problem, could you please retry the build with
revision 1.2 of common/include/prop/prop_object.h (and make sure
it gets installed before rebuilding)?  I think this revision
fixes the problem with redefined boolean_t.

Regards,

- H=E5vard