Don't serialize anything to a final kexe file. (#413)

That gives a little compilation speed improvement.

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/Context.kt

@@ -214,7 +214,7 @@ internal class Context(config: KonanConfig) : KonanBackendContext(config) {
     // right after the frontend.
     // But we have to wait until the code generation phase,
     // to dump this information into generated file.
-    lateinit var serializedLinkData: String
+    var serializedLinkData: String? = null
 
     // TODO: make lateinit?
     var irModule: IrModuleFragment? = null

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanPhases.kt

@@ -57,9 +57,12 @@ object KonanPhases {
         with (config.configuration) { with (KonanConfigKeys) { 
 
             // We disable inline IR deserialization
-            // until we have enough test passes
+            // until we have enough test passes.
             KonanPhase.DESERIALIZER.enabled = false
 
+            // Don't serialize anything to a final executable.
+            KonanPhase.SERIALIZER.enabled = getBoolean(NOLINK)
+
             val disabled = get(DISABLED_PHASES)
             disabled?.forEach { phases[known(it)]!!.enabled = false }
 

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/MetadataGenerator.kt

@@ -149,10 +149,12 @@ internal class MetadataGenerator(override val context: Context): ContextUtils {
     }
 
     private fun addLinkData(module: IrModuleFragment) {
+        val moduleAsString = context.serializedLinkData
+        if (moduleAsString == null) return
+
         val abiVersion = context.config.configuration.get(KonanConfigKeys.ABI_VERSION)
         val abiNode = metadataString("$abiVersion")
         val moduleName = metadataString(module.descriptor.name.asString())
-        val moduleAsString = context.serializedLinkData
         val dataNode = metadataString(moduleAsString)
 
         val kmetadataArg  = metadataNode(listOf(abiNode, moduleName, dataNode))