Fix @Retain annotation behavior. (#2068)

Interop/JsRuntime/src/main/kotlin/jsinterop.kt

@@ -25,10 +25,8 @@ typealias Object = Int
 typealias Pointer = Int
 
 /**
- * Used annotation is required to preserve functions
- * from internalization and DCE
+ * @Retain annotation is required to preserve functions from internalization and DCE.
  */
-
 @Retain
 @SymbolName("Konan_js_allocateArena")
 external public fun allocateArena(): Arena

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/IrToBitcode.kt

@@ -738,7 +738,7 @@ internal class CodeGeneratorVisitor(val context: Context, val lifetimes: Map<IrE
         }
 
 
-        if (declaration.descriptor.usedAnnotation) {
+        if (declaration.descriptor.retainAnnotation) {
             context.llvm.usedFunctions.add(codegen.llvmFunction(declaration))
         }
 

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/RetainAnnotation.kt

@@ -9,9 +9,9 @@ import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.descriptors.annotations.*
 import org.jetbrains.kotlin.name.FqName
 
-private val annotationName = FqName("kotlin.native.Used")
+private val annotationName = FqName("kotlin.native.Retain")
 
-internal val FunctionDescriptor.usedAnnotation: Boolean 
+internal val FunctionDescriptor.retainAnnotation: Boolean
     get() {
         return (this.annotations.findAnnotation(annotationName) != null)
     }