Add synthetic argument to default constructors

It's need to add synthetic argument (of type that user can't use)
to constructors with default arguments to avoid clashing with
real user's constructor having the same set of parameters
and additional int's arguments.

compiler/testData/codegen/box/secondaryConstructors/clashingDefaultConstructors.kt

@@ -0,0 +1,35 @@
+open class A(val x: String = "abc", val y: String = "efg") {
+    constructor(x: String, y: String, z: Int): this(x, y + "#" + z.toString()) {}
+    
+    override fun toString() = "$x#$y"
+}
+
+class B : A {
+    constructor(x: String, y: String, z: Int): super(x, y + z.toString()) {}
+    constructor(x: String = "xyz", y: String = "123") : super(x, y)  {}
+    constructor(x: Double): super(x.toString()) {}
+}
+
+fun box(): String {
+    val a1 = A().toString()
+    if (a1 != "abc#efg") return "fail1: $a1"
+
+    val a2 = A("hij", "klm", 1).toString()
+    if (a2 != "hij#klm#1") return "fail2: $a2"
+
+    val a3 = A(x="xyz").toString()
+    if (a3 != "xyz#efg") return "fail3: $a3"
+
+    val b1 = B().toString()
+    if (b1 != "xyz#123") return "fail4: $b1"
+
+    val b2 = B("hij", "klm", 2).toString()
+    if (b2 != "hij#klm2") return "fail5: $b2"
+
+    val b3 = B(123.0).toString()
+    if (b3 != "123.0#efg") return "fail6: $b3"
+
+    val b4 = B(x="test").toString()
+    if (b4 != "test#123") return "fail7: $b4"
+    return "OK"
+}