Fix casts of Unit value to other types

compiler/testData/codegen/box/casts/asAny.kt

@@ -1,7 +0,0 @@
-fun println(s: String) {
-}
-
-fun box(): String {
-    println(":Hi!") as Any
-    return "OK"
-}

compiler/testData/codegen/box/casts/unitAsAny.kt

@@ -0,0 +1,8 @@
+fun println(s: String) {
+}
+
+fun box(): String {
+    val x = println(":Hi!") as Any
+    if (x != Unit) return "Fail: $x"
+    return "OK"
+}

compiler/testData/codegen/box/casts/unitAsSafeAny.kt

@@ -0,0 +1,8 @@
+fun println(s: String) {
+}
+
+fun box(): String {
+    val x = println(":Hi!") as? Any
+    if (x != Unit) return "Fail: $x"
+    return "OK"
+}

compiler/testData/codegen/boxWithStdlib/casts/unitAsInt.kt

@@ -0,0 +1,15 @@
+fun foo() {}
+
+fun box(): String {
+    try {
+        foo() as Int?
+    }
+    catch (e: ClassCastException) {
+        return "OK"
+    }
+    catch (e: Throwable) {
+        return "Fail: ClassCastException should have been thrown, but was instead ${e.javaClass.getName()}: ${e.getMessage()}"
+    }
+
+    return "Fail: no exception was thrown"
+}