Implement lowering of some builtin operators. (#154)

* EQEQ
* THROW_NPE

Add test for (un)boxing `==` operands.

backend.native/tests/codegen/boxing/boxing13.kt

@@ -0,0 +1,10 @@
+fun is42(x: Any?) {
+    println(x == 42)
+    println(42 == x)
+}
+
+fun main(args: Array<String>) {
+    is42(16)
+    is42(42)
+    is42("42")
+}