Disallow having a value classe whose underlying value is itself

[helloqirun]

dotc crashes when compiling the follow code.

$ cat abc.scala

class Test2(val valueVal: Test2) extends AnyVal

$ dotc abc.scala
output:
https://gist.github.com/helloqirun/d09e36c276832140e7c74d1f26378a14

[smarter]

Since the error message contains 989 lines, I have cut most of lines.

For very long output, you can paste them on https://gist.github.com/ and put a link in your issue.

[helloqirun]

Thanks, updated.