Native build: don't read klib files in KonanCacheTask.cacheFile

It is `@OutputDirectory`, so Gradle can invoke it early, even before the
klib itself is built.

Instead of reading `uniqName` from klib files, require specifying it
explicitly.

kotlin-native/runtime/build.gradle.kts

@@ -512,6 +512,7 @@ targetList.forEach { targetName ->
         tasks.register("${targetName}StdlibCache", KonanCacheTask::class.java) {
             target = targetName
             originalKlib = project.buildDir.resolve("${targetName}Stdlib")
+            klibUniqName = "stdlib"
             cacheRoot = project.buildDir.resolve("cache/$targetName").absolutePath
 
             dependsOn("${targetName}Stdlib")