kristenk authored May 05, 2018 and Mikhail Glushenkov committed May 09, 2018

This commit generalizes the fix for issue #4781
(e86f8389) by tracking dependencies on
components instead of dependencies on executables.  That means that the solver
always checks whether a package contains a library before using it to satisfy a
build-depends dependency.  If a version of a package doesn't contain a library,
the solver can try other versions.  Associating each dependency with a component
also moves towards the design for component-based dependency solving described
in issue #4087.