While Javac honors annotation processors, various CompilationParticipant
(such as PDE's  DSAnnotationCompilationParticipant) don't pass a
compiler-level annotation processor to the compiler, being no-op in
compilation, and are then expected to proceed upon completion of the
compilation, even with Javac.

This patch refines the condition for a CompilationParticipant to
participate (or more precisely the other way round, it refines the
conditions for a CompilationParticipant to not processAnnotations)