[interop] Prepare interop driver for a metadata-only mode.

utilities/src/main/kotlin/org/jetbrains/kotlin/cli/utilities/GeneratePlatformLibraries.kt

@@ -83,7 +83,7 @@ private fun generatePlatformLibraries(target: String, inputDirectory: File, outp
                 "-no-default-libs", "-no-endorsed-libs", "-Xpurge-user-libs",
                 *def.depends.flatMap { listOf("-l", "$outputDirectory/${it.name}") }.toTypedArray())
         println("Processing ${def.name}...")
-        K2Native.mainNoExit(invokeInterop("native", args))
+        invokeInterop("native", args)?.let { K2Native.mainNoExit(it) }
         org.jetbrains.kotlin.cli.klib.main(arrayOf("install", outKlib,
                 "-target", target,
                 "-repository", "${outputDirectory.absolutePath}"

utilities/src/main/kotlin/org/jetbrains/kotlin/cli/utilities/InteropCompiler.kt

@@ -19,7 +19,11 @@ import org.jetbrains.kotlin.native.interop.tool.*
 // TODO: this function should eventually be eliminated from 'utilities'. 
 // The interaction of interop and the compiler should be streamlined.
 
-fun invokeInterop(flavor: String, args: Array<String>): Array<String> {
+/**
+ * @return null if there is no need in compiler invocation.
+ * Otherwise returns array of compiler args.
+ */
+fun invokeInterop(flavor: String, args: Array<String>): Array<String>? {
     val arguments = if (flavor == "native") CInteropArguments() else JSInteropArguments()
     arguments.argParser.parse(args)
     val outputFileName = arguments.output
@@ -68,7 +72,9 @@ fun invokeInterop(flavor: String, args: Array<String>): Array<String> {
         additionalProperties.putAll(mapOf("cstubsname" to cstubsName, "import" to imports))
     }
 
+
     val cinteropArgsToCompiler = interop(flavor, args + additionalArgs, additionalProperties)
+            ?: return null // There is no need in compiler invocation if we're generating only metadata.
 
     val nativeStubs = 
         if (flavor == "wasm") 

utilities/src/main/kotlin/org/jetbrains/kotlin/cli/utilities/main.kt

@@ -17,11 +17,11 @@ private fun mainImpl(args: Array<String>, konancMain: (Array<String>) -> Unit) {
             konancMain(utilityArgs)
         "cinterop" -> {
             val konancArgs = invokeInterop("native", utilityArgs)
-            konancMain(konancArgs)
+            konancArgs?.let { konancMain(it) }
         }
         "jsinterop" -> {
             val konancArgs = invokeInterop("wasm", utilityArgs)
-            konancMain(konancArgs)
+            konancArgs?.let { konancMain(it) }
         }
         "klib" ->
             klibMain(utilityArgs)