Support Void.TYPE as underlying Class object for KClass

#KT-20875 Fixed

compiler/testData/codegen/box/classLiteral/java/javaPrimitiveType.kt

@@ -50,14 +50,15 @@ fun box(): String {
     check(Double::class.javaPrimitiveType, "double")
     check(Double::class, "double")
 
+    check(Void::class.javaPrimitiveType, "void")
+    check(Void::class, "void")
+
     checkNull(String::class.javaPrimitiveType)
     checkNull(String::class)
 
-    checkNull(Nothing::class.javaPrimitiveType)
-    checkNull(Nothing::class)
-
-    checkNull(Void::class.javaPrimitiveType)
-    checkNull(Void::class)
+    // TODO: KT-15518
+    check(Nothing::class.javaPrimitiveType, "void")
+    check(Nothing::class, "void")
 
     return "OK"
 }

compiler/testData/codegen/box/classLiteral/java/javaPrimitiveTypeReified.kt

@@ -26,9 +26,9 @@ fun box(): String {
     check<Float>("float")
     check<Long>("long")
     check<Double>("double")
+    check<Void>("void")
 
     checkNull<String>()
-    checkNull<Void>()
 
     return "OK"
 }