Mihail Konev authored Dec 29, 2016 and Adam Jackson committed Jan 02, 2017

The custom os/os.O library reuses *.o files of os/libos.la.

The current rule assumes automake puts all the objects into per-target
am__*_la_OBJECTS variable.  At least with AC_REPLACE_FUNCS, this no
longer holds (as wanted objects are put into LTLIBOBJS instead).

Depend on automake's result, the *.la library instead, to express demand
of any its dependencies being built.

Should be fixing randomly occuring "undefined reference to `strlcpy'"
errors when linking Xvfb and other DDX-es that could use os.O.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Mihail Konev <k.mvc@ya.ru>