Restore help msg for other than language

[Cherry-picked 929e7eb]

Author: som-snytt

compiler/src/dotty/tools/dotc/config/CompilerCommand.scala

@@ -9,7 +9,8 @@ abstract class CompilerCommand extends CliCommand:
 
   final def helpMsg(using settings: ConcreteSettings)(using SettingsState, Context): String =
     settings.allSettings.find(isHelping) match
-      case Some(s) => availableOptionsMsg(_ == s, showArgFileMsg = false)
+      case Some(s @ settings.language) => availableOptionsMsg(_ == s, showArgFileMsg = false)
+      case Some(s) => s.description
       case _ =>
         if (settings.help.value) usageMessage
         else if (settings.Vhelp.value) vusageMessage