The ValueObject library doesn't actually depend on any plugins
currently, but it links against the C++ and ObjC language plugins. I
removed those and added NO_PLUGIN_DEPENDENCIES.
However, the build failed initally because the Commands library depends
on clangFrontend and it was previously getting it transitively through
ValueObject -> C++/ObjC Language -> clangFrontend. This makes the
dependency more explicit.
45d5e7baba