Fix build failure after merging #1492
Fix build failure after merging #1492

The one-parameter constructor of SourceFile was removed in #1494

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