-d /tmp on macos fails

[som-snytt]

minimized code

$ dotc -d /tmp hello.scala
Error while emitting hello.scala
exception occurred while compiling hello.scala
java.nio.file.FileAlreadyExistsException: /tmp while compiling hello.scala
Exception in thread "main" java.nio.file.FileAlreadyExistsException: /tmp

expectation

Fixed as in scala 2.
scala/scala#6450

[som-snytt]

#8094