Update MSVC macro to remove condition duplication

Repeating the conditions is a bit annoying, and error-prone; use some
macro programming to elimate the duplication.

Author: jagerman

include/pybind11/pybind11.h

@@ -825,11 +825,18 @@ class class_ : public detail::generic_type {
     template <typename T> using is_base_class = detail::bool_constant<std::is_base_of<T, type_>::value && !std::is_same<T, type_>::value>;
 #if defined(_MSC_VER) // MSVC fails with the below type alias, unable to find the is_holder, is_subtype, etc. predicate types
     template <typename T> struct is_valid_class_option :
-        detail::bool_constant<is_holder<T>::value || is_subtype<T>::value || is_base_class<T>::value> {};
 #else
     template <typename T> using is_valid_class_option =
-        detail::bool_constant<is_holder<T>::value || is_subtype<T>::value || is_base_class<T>::value>;
 #endif
+        detail::bool_constant<
+            is_holder<T>::value ||
+            is_subtype<T>::value ||
+            is_base_class<T>::value
+        >
+#if defined(_MSC_VER)
+            {}
+#endif
+            ;
 
     using extracted_holder_t = typename detail::first_of_t<is_holder, options...>;