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/shared/build.gradle.kts

@@ -41,7 +41,7 @@ sourceSets["main"].withConvention(KotlinSourceSet::class) {
 
 tasks.withType<KotlinCompile> {
     kotlinOptions.jvmTarget = "1.8"
-    kotlinOptions.freeCompilerArgs = listOf("-Xskip-prerelease-check")
+    kotlinOptions.freeCompilerArgs += listOf("-Xskip-prerelease-check")
 }
 
 tasks.jar {