Fix :kotlin-native:**:nativelibs Gradle tasks

These tasks did copy all files from build to build/nativelibs, thus
causing up-to-date checks to fail, and native libs and temporary build
files to be accumulated in recursive directories like
nativelibs/nativelibs/... in both build dirs and dist.

Fix this by copying only relevant files.

kotlin-native/Interop/Indexer/build.gradle.kts

@@ -144,9 +144,10 @@ dependencies {
 }
 
 val nativelibs = project.tasks.create<Copy>("nativelibs") {
-    dependsOn(solib("clangstubs"))
+    val clangstubsSolib = solib("clangstubs")
+    dependsOn(clangstubsSolib)
 
-    from("$buildDir/")
+    from("$buildDir/$clangstubsSolib")
     into("$buildDir/nativelibs/")
 }
 

kotlin-native/Interop/Runtime/build.gradle.kts

@@ -86,8 +86,9 @@ tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach
 
 
 val nativelibs = project.tasks.create<Copy>("nativelibs") {
-    dependsOn(solib("callbacks"))
+    val callbacksSolib = solib("callbacks")
+    dependsOn(callbacksSolib)
 
-    from("$buildDir/")
+    from("$buildDir/$callbacksSolib")
     into("$buildDir/nativelibs/")
 }