Add the sources of scalajs-ir to dotty instead of its binaries.
Add the sources of scalajs-ir to dotty instead of its binaries.

This guarantees that we can bootstrap dotty without depending on
the binaries of scalajs-ir compiled by another Scala compiler.

lampepfl/dotty,sjrd/dotty,sjrd/dotty,som-snytt/dotty,dotty-staging/dotty,som-snytt/dotty,sjrd/dotty,lampepfl/dotty,som-snytt/dotty,dotty-staging/dotty,lampepfl/dotty,sjrd/dotty,lampepfl/dotty,dotty-staging/dotty,dotty-staging/dotty,sjrd/dotty,som-snytt/dotty,lampepfl/dotty,dotty-staging/dotty,som-snytt/dotty