Hide sigh warnings about linking existing files (#4486)
Hide sigh warnings about linking existing files (#4486)

* Hide sigh warnings about linking existing files

* Improvements to types for makeLink's options value

* Lint fix

PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs