Where a module provides a single feature, and that feature is disabled (./configure --without-foo), the DSO is still produced, but without (meaningful) code. Would it be much work to change this so that no such dummy modules would be built?

Furthermore, if a feature is requested but the configure script can't find the required headers or libraries, the sole effect is to disable the feature. Although it's possible to programatically check what features have actually been built, I think it would be better if the build would fail in case of problems, or if at least the corresponding files would not be produced.