Make project C++20 compatible

Samples/basic/demo/src/main.cpp

@@ -370,7 +370,10 @@ public:
 			if (el_rating && el_rating_emoji)
 			{
 				enum { Sad, Mediocre, Exciting, Celebrate, Champion, CountEmojis };
-				static const Rml::Core::String emojis[CountEmojis] = { u8"😢", u8"😐", u8"😮", u8"😎", u8"🏆" };
+				static const Rml::Core::String emojis[CountEmojis] = { 
+					(const char*)u8"😢", (const char*)u8"😐", (const char*)u8"😮",
+					(const char*)u8"😎", (const char*)u8"🏆"
+				};
 				int value = event.GetParameter("value", 50);
 				
 				Rml::Core::String emoji;