Do not reset freeCompilerArgs for some kotlin-native modules

Otherwise common compiler arguments which are set for all modules in the
project in `buildSrc/src/main/kotlin/common-configuration.gradle.kts`
are not applied. The most interesting of those are `-Xuse-k2` (if K2 is
enabled) and `-Xjvm-default=all`.

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

@@ -46,9 +46,9 @@ dependencies {
 tasks {
     withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile> {
         kotlinOptions {
-            freeCompilerArgs = listOf(
-                    "-opt-in=kotlin.ExperimentalUnsignedTypes",
-                    "-Xskip-metadata-version-check"
+            freeCompilerArgs += listOf(
+                "-opt-in=kotlin.ExperimentalUnsignedTypes",
+                "-Xskip-metadata-version-check"
             )
             allWarningsAsErrors = true
         }