Do not use UnusedCommon directly

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/Flags.scala

@@ -361,6 +361,7 @@ object Flags {
   /** Labeled with `unused` modifier (unused value)  */
   final val UnusedCommon = commonFlag(42, "unused")
   final val Unused = UnusedCommon.toTermFlags
+  final val UnusedType = UnusedCommon.toTypeFlags
 
   // Flags following this one are not pickled
 

compiler/src/dotty/tools/dotc/transform/UnusedChecks.scala

@@ -25,7 +25,7 @@ class UnusedChecks extends MiniPhase {
   /* Tree transform */
 
   override def transformTypeDef(tree: TypeDef)(implicit ctx: Context): tree.type = {
-    if (tree.symbol.is(UnusedCommon))
+    if (tree.symbol.is(UnusedType))
       ctx.error(tree.symbol.showKind + " cannot be unused", tree.pos)
     tree
   }