// transitively imported by the whole program; addTransitiveLinkDeps
// makes sure those are present in a.Deps.
// If shlib is non-empty, then a corresponds to the build and installation of shlib,
// so any rebuild of shlib should not be added as a dependency.
func (b *Builder) addTransitiveLinkDeps(a, a1 *Action, shlib string) {
	// Expand Deps to include all built packages, for the linker.