Rework stubs for interop globals passed by value

#KT-21855 Fixed

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

@@ -52,3 +52,6 @@ void invoke2(void (^block)(void)) {
 
 int (^getSupplier(int x))(void);
 Class (^ _Nonnull getClassGetter(NSObject* obj))(void);
+
+extern NSString* globalString;
+extern NSObject* globalObject;

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

@@ -48,6 +48,18 @@ fun run() {
         // toString (virtually):
         println(map.keys.map { it.toString() }.min() == foo.description())
     }
+
+    println(globalString)
+    autoreleasepool {
+        globalString = "Another global string"
+    }
+    println(globalString)
+
+    println(globalObject)
+    globalObject = object : NSObject() {
+        override fun description() = "global object"
+    }
+    println(globalObject)
 }
 
 fun MutablePairProtocol.swap() {

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

@@ -57,3 +57,6 @@ int (^getSupplier(int x))(void) {
 Class (^ _Nonnull getClassGetter(NSObject* obj))() {
     return ^{ return obj.class; };
 }
+
+NSString* globalString = @"Global string";
+NSObject* globalObject = nil;