Fix fixed NSString* parameters in variadic functions

backend.native/tests/interop/objc/smoke.h

@@ -55,3 +55,5 @@ Class (^ _Nonnull getClassGetter(NSObject* obj))(void);
 
 extern NSString* globalString;
 extern NSObject* globalObject;
+
+int formatStringLength(NSString* format, ...);

backend.native/tests/interop/objc/smoke.kt

@@ -60,6 +60,8 @@ fun run() {
         override fun description() = "global object"
     }
     println(globalObject)
+
+    println(formatStringLength("%d %d", 42, 17))
 }
 
 fun MutablePairProtocol.swap() {

backend.native/tests/interop/objc/smoke.m

@@ -60,3 +60,11 @@ Class (^ _Nonnull getClassGetter(NSObject* obj))() {
 
 NSString* globalString = @"Global string";
 NSObject* globalObject = nil;
+
+int formatStringLength(NSString* format, ...) {
+  va_list args;
+  va_start(args, format);
+  NSString* result = [[NSString alloc] initWithFormat:format arguments:args];
+  va_end(args);
+  return result.length;
+}