Set the correct enum integer type in GenerateEnumFromMacros.

src/Generator/Library.cs

@@ -186,13 +186,39 @@ namespace CppSharp
 
             if (@enum.Items.Count > 0)
             {
+                @enum.BuiltinType = new BuiltinType(GetUnderlyingTypeForEnumValue(maxValue));
+                @enum.Type = @enum.BuiltinType;
                 @enum.Namespace = unitToAttach;
+
                 unitToAttach.Declarations.Add(@enum);
             }
 
             return @enum;
         }
 
+        private static PrimitiveType GetUnderlyingTypeForEnumValue(ulong maxValue)
+        {
+            if (maxValue < (byte)sbyte.MaxValue)
+                return PrimitiveType.SChar;
+
+            if (maxValue < byte.MaxValue)
+                return PrimitiveType.UChar;
+
+            if (maxValue < (ushort)short.MaxValue)
+                return PrimitiveType.Short;
+
+            if (maxValue < ushort.MaxValue)
+                return PrimitiveType.UShort;
+
+            if (maxValue < int.MaxValue)
+                return PrimitiveType.Int;
+
+            if (maxValue < uint.MaxValue)
+                return PrimitiveType.UInt;
+
+            throw new NotImplementedException();
+        }
+
         #endregion
 
         #region Class Helpers