[JS IR DCE] Add CLI option to print reachability info

compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/K2JsIrCompiler.kt

@@ -1,6 +1,6 @@
 /*
- * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
- * that can be found in the license/LICENSE.txt file.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.cli.js
@@ -317,6 +317,8 @@ class K2JsIrCompiler : CLICompiler<K2JSCompilerArguments>() {
         if (!arguments.sourceMap && sourceMapEmbedContentString != null) {
             messageCollector.report(WARNING, "source-map-embed-sources argument has no effect without source map", null)
         }
+
+        configuration.put(JSConfigurationKeys.PRINT_REACHABILITY_INFO, arguments.irDcePrintReachabilityInfo)
     }
 
     override fun executableScriptFileName(): String {