With --disable-xorg, We also disabled a bunch of tests because of their
perceived reliance on a DDX. The cause was libtool missing some object files
that never ended up in libxservertest.la. Only the xfree86 test has a true
dependency on XORG.

DIX_LIB was pointing to dix.O (instead of libdix.la) when
DTRACE_SPECIAL_OBJECTS was defined. libdix.la should be part of XSERVER_LIBS
but dix.O is not a recognised libtool object, so it got skipped for
libxservertest.a. Only in the XORG case would we add DIX_LIB and OS_LIB
manually, thus forcing linkage with the dtrace-generated objects.

Fixing this by packaging up the dtrace-generated files as part of
libdix.la/libos.la doesn't work for Solaris (and possible others), so simply
always force linkage against the DIX_LIB/OS_LIB in the case of dtrace objects.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Tested-by: Alan Coopersmith <alan.coopersmith@oracle.com>