Switch with alternatives crashes

[nicolasstucki]

val a: Int = 4
a match {
  case 1 => println("1")
  case 1 | 2 => println("1 or 2")
}

crashes with

duplicate keys in SWITCH, can't pick arbitrarily one of them to evict, see SI-6011.
java.lang.RuntimeException: duplicate keys in SWITCH, can't pick arbitrarily oneof them to evict, see SI-6011.
        at dotty.tools.backend.jvm.DottyBackendInterface.abort(DottyBackendInterface.scala:390)
        at scala.tools.nsc.backend.jvm.BCodeIdiomatic$JCodeMethodN.emitSWITCH(BCodeIdiomatic.scala:477)
        at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genMatch(BCodeBodyBuilder.scala:909)
        at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:431)

[andrevidela]

@liufengyun I have a pull request incoming for this fix that I did during last weekend's Scala spree. Could I take care of this?

[smarter]

@andrevidela Yes no problem, I'll assign myself to this issue and I'll review your PR once it's open.