[K/N] Convert :kotlin-native:klib

Use folder structure from the rest of the project and build it by
the bootstrap compiler.

kotlin-native/klib/build.gradle.kts

@@ -1,17 +1,7 @@
-buildscript {
-    apply(from = "$rootDir/kotlin-native/gradle/kotlinGradlePlugin.gradle")
-}
-
 plugins {
     kotlin("jvm")
 }
 
-repositories {
-    extra["bootstrapKotlinRepo"]?.let {
-        maven(url = it)
-    }
-}
-
 dependencies {
     implementation(project(":core:descriptors"))
     implementation(project(":native:frontend.native"))
@@ -23,6 +13,7 @@ dependencies {
     implementation(project(":kotlin-metadata")) { isTransitive = false }
 }
 
-tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompilationTask<*>> {
-    compilerOptions.freeCompilerArgs.add("-Xskip-prerelease-check")
-}
+sourceSets {
+    "main" { projectDefault() }
+    "test" { none() }
+}