Fix path seperator problem on Windows of Gradle generateCMake task (#1657)

Signed-off-by: Charlie Jiang <cqjjjzr@126.com>

tools/kotlin-native-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/tasks/KonanGenerateCMakeTask.kt

@@ -123,7 +123,7 @@ open class KonanGenerateCMakeTask : DefaultTask() {
         }.joinToString(" ")
 
     private val KonanCompileTask.cMakeLinkerOpts: String
-        get() = linkerOpts.joinToString(" ")
+        get() = linkerOpts.joinToString(" ").replace('\\', '/')
 }
 
 private class Call(val name: String) {