Added test on function overriding return type with Unit

backend.native/tests/build.gradle

@@ -688,6 +688,11 @@ task bridges_test17(type: RunKonanTest) {
     source = "codegen/bridges/test17.kt"
 }
 
+task bridges_test18(type: RunKonanTest) {
+    goldValue = "kotlin.Unit\n"
+    source = "codegen/bridges/test18.kt"
+}
+
 task bridges_linkTest(type: LinkKonanTest) {
     goldValue = "42\n42\n42\n"
     source = "codegen/bridges/linkTest_main.kt"

backend.native/tests/codegen/bridges/test18.kt

@@ -0,0 +1,13 @@
+// overriden function returns Unit
+open class A {
+    open fun foo(): Any = 42
+}
+
+open class B: A() {
+    override fun foo(): Unit { }
+}
+
+fun main(args: Array<String>) {
+    val a: A = B()
+    println(a.foo())
+}