Add missing overload for is function to handle enums

Author: filipsajdak

include/cpp2util.h

@@ -548,6 +548,11 @@ auto is( X const& x ) -> bool {
     return x == X();
 }
 
+template< auto value, typename X >
+    requires std::is_enum_v<decltype(value)> && std::is_same_v<decltype(value),X>
+auto is( X const& x ) -> bool {
+    return x == value;
+}
 
 //-------------------------------------------------------------------------------------------------------------
 //  Built-in as (partial)