[CMake] ambiguous ALL status for aux build target

[Brad Aisa]

Our project includes some custom source file generation steps -- these work 
fine. We also added some custom targets to force building of these targets, 
and to clean them. Those targets are defined like this:

add_custom_target(force_ta_xxx
   COMMAND [the command to force building it...]
)
add_custom_target(fclean_ta_xxx
   COMMAND [the command to delete it...]
)

Then, in our top-level master file, we had an overall guy to do all these 
particular guys:

add_custom_target(force_ta
   DEPENDS force_ta_cs, force_ta_so [etc.]
)

And likewise for clean

The thing is that in VS 9, some of these targets end up appearing in the 
default build. If I don't make an overall guy, then the force_ta_xxx guys 
aren't in the default build, but confusingly, the clean_ta_xxx guys are. As 
soon as I introduce the top guy, the component guys automatically get 
marked as included, but the top guy sometimes does, sometimes doesn't. I 
haven't been able to figure out why -- note I haven't put "ALL" in those 
targets. Can someone offer some clues?

Thanks!