[gradle][plugin] debug build option is introduced.

there're two optons:
1. add enableDebug option in the build.gradle:

konanArtifacts {
    CsvParser {
        enableDebug true
        ...
    }
}

2. specify in command line with project properties -PenableDebug=true

tools/kotlin-native-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KonanCompileTask.kt

@@ -116,6 +116,8 @@ open class KonanCompileTask: KonanTargetableTask() {
     @Input var linkerOpts = mutableListOf<String>()
         internal set
 
+    @Input var enableDebug        = project.properties.containsKey("enableDebug") && project.properties["enableDebug"].toString().toBoolean()
+        internal set
     @Input var noStdLib           = false
         internal set
     @Input var noMain             = false
@@ -149,6 +151,7 @@ open class KonanCompileTask: KonanTargetableTask() {
         addArgIfNotNull("-language-version", languageVersion)
         addArgIfNotNull("-api-version", apiVersion)
 
+        addKey("-g", enableDebug)
         addKey("-nostdlib", noStdLib)
         addKey("-nomain", noMain)
         addKey("-opt", enableOptimization)
@@ -209,6 +212,7 @@ open class KonanCompileConfig(
         anotherTask.apiVersion?.let { apiVersion(it) }
         anotherTask.produce.let { produce(it) }
 
+        enableDebug(anotherTask.enableDebug)
         if (anotherTask.noStdLib) noStdLib()
         if (anotherTask.noMain) noMain()
         if (anotherTask.enableOptimization) enableOptimization()
@@ -291,6 +295,10 @@ open class KonanCompileConfig(
         apiVersion = version
     }
 
+    fun enableDebug(flag: Boolean) = with(compilationTask) {
+        enableDebug = flag
+    }
+
     fun noStdLib() = with(compilationTask) {
         noStdLib = true
     }

tools/kotlin-native-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KonanPlugin.kt

@@ -148,6 +148,7 @@ internal fun dumpProperties(task: Task) {
             println("libraries          : ${task.libraries}")
             println("nativeLibraries    : ${task.nativeLibraries}")
             println("linkerOpts         : ${task.linkerOpts}")
+            println("enableDebug        : ${task.enableDebug}")
             println("noStdLib           : ${task.noStdLib}")
             println("noMain             : ${task.noMain}")
             println("enableOptimization : ${task.enableOptimization}")