FIR: set anonymous object constructor return type properly

compiler/testData/codegen/box/defaultArguments/constructor/kt30517.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 
 open class Foo(val args: String){
     constructor(arg: Any = 1) : this(arg.toString()) {

compiler/testData/codegen/box/defaultArguments/constructor/objectExpressionDelegatingToSecondaryConstructor.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 
 abstract class O(val value: String) {
     constructor(o: Char = 'O') : this("$o")