8152650: ModuleFinder.compose should accept varargs

[Alan Bateman]

There are several patches that didn't go in with the last update, the 
change to ModuleFinder.compose to use varargs was one of them. The other 
part to this is removing the empty() method as it is redundant. The 
changes are straight-forward:
   http://cr.openjdk.java.net/~alanb/8152650/webrev/

I dropped the changes to the langtools repo as Jon/Vicente have a patch 
in flight that drops empty(). Also the last round of jdeps updates 
removed the use of empty().

-Alan.