This adds a new attribute to Dependency that allows consumers to choose
to not link a dependency. This is useful for if you have this dependency
tree with static libraries:
App -> A -> Shared
App -> B -> Shared
Where A and B both share a static library dependency, that is finally
linked into App. If Shared is added to the link phase of A and B, you
end up with duplicate symbols during the link phase. With this change
consumers could set link: False on A and B's dependency on Shared, this
way Shared will get build before A and B, but not linked.
Keith Smiley
Brandon Kase
Yonas Kolb