allow type initializers to be 'async'

implicit calls to an async super.init are not allowed

lib/Sema/DerivedConformanceCodingKey.cpp

@@ -130,6 +130,7 @@ static ValueDecl *deriveInitDecl(DerivedConformance &derived, Type paramType,
   auto *initDecl =
     new (C) ConstructorDecl(name, SourceLoc(),
                             /*Failable=*/true, /*FailabilityLoc=*/SourceLoc(),
+                            /*Async=*/false, /*AsyncLoc=*/SourceLoc(),
                             /*Throws=*/false, /*ThrowsLoc=*/SourceLoc(),
                             paramList,
                             /*GenericParams=*/nullptr, parentDC);