Detect types convertible to unformattable pointers

include/fmt/core.h

@@ -1370,8 +1370,11 @@ template <typename Context> struct arg_mapper {
 
   // We use SFINAE instead of a const T* parameter to avoid conflicting with
   // the C array overload.
-  template <typename T, FMT_ENABLE_IF(std::is_pointer<T>::value)>
-  FMT_CONSTEXPR auto map(T) -> unformattable_pointer {
+  template <
+      typename T,
+      FMT_ENABLE_IF(std::is_convertible<const T&, const void*>::value &&
+                    !std::is_convertible<const T&, const char_type*>::value)>
+  FMT_CONSTEXPR auto map(const T&) -> unformattable_pointer {
     return {};
   }