Skip Function1-3 in specializing child classes

Author: liufengyun

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

@@ -33,7 +33,7 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
       var arity = 0
       while (arity < 3) {
         val func = defn.FunctionClass(arity)
-        if (sym.derivesFrom(func)) {
+        if (sym != func && sym.derivesFrom(func)) {
           val baseType   = tp.cls.typeRef.baseType(func)
           val paramTypes = baseType.argInfos
           val argTypes   = paramTypes.init