Use correct LanguageVersionSettings in MetadataSerializer

Also, require users of K2MetadataCompiler to pass "-Xmulti-platform"
manually. Gradle and Maven plugins already do that, so only users who
invoke kotlinc directly are going to be affected by this

 #KT-19287 Fixed

compiler/tests-common/org/jetbrains/kotlin/checkers/AbstractDiagnosticsTest.kt

@@ -291,7 +291,7 @@ abstract class AbstractDiagnosticsTest : BaseDiagnosticsTest() {
         val platform = moduleDescriptor.getMultiTargetPlatform()
         if (platform == MultiTargetPlatform.Common) {
             return DefaultAnalyzerFacade.analyzeFiles(
-                    files, moduleDescriptor.name, true,
+                    files, moduleDescriptor.name, true, languageVersionSettings,
                     mapOf(
                             MultiTargetPlatform.CAPABILITY to MultiTargetPlatform.Common,
                             MODULE_FILES to files