Support OptionalExpectation in serializer (#2048)

* [serializer] Support OptionalExpectation

* Fix OptionalExectation test for Windows

* [tests] Don't print compiler args by default

backend.native/tests/build.gradle

@@ -2317,7 +2317,7 @@ task mpp_optional_expectation(type: RunStandaloneKonanTest) {
     def outputRoot = project.ext."$outputSourceSetName"
     flags = [
             '-Xmulti-platform',
-            "-Xcommon-sources=${file("$outputRoot/$name/mpp_optional_expectation.kt")}"
+            "-Xcommon-sources=$outputRoot/$name/mpp_optional_expectation.kt"
     ]
 }
 

backend.native/tests/codegen/mpp/mpp_optional_expectation.kt

@@ -1,10 +1,17 @@
 @file:Suppress("EXPERIMENTAL_API_USAGE_ERROR")
+
+import kotlin.js.*
+
 @OptionalExpectation
 expect annotation class Optional()
 
 @Optional
 fun foo() { println(42) }
 
+@JsName("jsBar")
+fun bar() { println(43) }
+
 fun main(args: Array<String>) {
     foo()
+    bar()
 }