The .sdg/.sdv/.thm files are generated by gengal (i.e. the
Gallery_get_target) but are not targets, which means they will only be
delivered in a second make invocation because make requires running a
command to propagate out-of-date-ness.

Change-Id: Iddb2222151bdbcf93d79bd801fa30ab7d7fbd1d3