backend: add tests:

* test for uninitialized vals
* test initializers3: global `var` of reference type
* expression_as_statement (disabled): using type operator as statement

Also enable test break1.

backend.native/tests/codegen/basics/expression_as_statement.kt

@@ -0,0 +1,14 @@
+fun foo() {
+    Any() as String
+}
+
+fun main(args: Array<String>) {
+    try {
+        foo()
+    } catch (e: Throwable) {
+        println("Ok")
+        return
+    }
+
+    println("Fail")
+}