Improve ATL/MFC string input support for C++11 ... C++17

Add support for any strings derived from CSimpleStringT when using C++11
... C++17 compilers.

include/upa/str_arg.h

@@ -59,6 +59,13 @@ struct is_size_type : std::integral_constant<bool,
     std::is_convertible<SizeT, std::ptrdiff_t>::value
 > {};
 
+// See: https://en.cppreference.com/w/cpp/concepts/derived_from
+template<class Derived, class Base>
+struct is_derived_from : std::integral_constant<bool,
+    std::is_base_of<Base, Derived>::value &&
+    std::is_convertible<const volatile Derived*, const volatile Base*>::value
+> {};
+
 
 // string args helper class
 

include/upa/url_for_atl.h

@@ -14,7 +14,7 @@
 #ifdef UPA_CPP_20
 # include <concepts>
 #else
-# include <cstringt.h>
+# include <type_traits>
 #endif
 
 namespace upa {
@@ -43,17 +43,14 @@ struct str_arg_char<StrT> : public str_arg_char_for_atl<StrT> {};
 
 #else // UPA_CPP_20
 
-template<typename CharT, bool mfcdll>
-struct str_arg_char<ATL::CSimpleStringT<CharT, mfcdll>> :
-    public str_arg_char_for_atl<ATL::CSimpleStringT<CharT, mfcdll>> {};
-
-template<typename CharT, class StringTraits>
-struct str_arg_char<ATL::CStringT<CharT, StringTraits>> :
-    public str_arg_char_for_atl<ATL::CStringT<CharT, StringTraits>> {};
-
-template<class StrT, int nChars>
-struct str_arg_char<ATL::CFixedStringT<StrT, nChars>> :
-    public str_arg_char_for_atl<ATL::CFixedStringT<StrT, nChars>> {};
+// CStringT and CFixedStringT are derived from CSimpleStringT
+template<class StrT>
+struct str_arg_char<StrT, typename std::enable_if<
+    is_derived_from<StrT, ATL::CSimpleStringT<char, true>>::value ||
+    is_derived_from<StrT, ATL::CSimpleStringT<wchar_t, true>>::value ||
+    is_derived_from<StrT, ATL::CSimpleStringT<char, false>>::value ||
+    is_derived_from<StrT, ATL::CSimpleStringT<wchar_t, false>>::value
+    >::type> : public str_arg_char_for_atl<StrT> {};
 
 #endif // UPA_CPP_20