Use std::allocator_traits (#3804)

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

include/fmt/format.h

@@ -43,9 +43,13 @@
 #include <cstring>           // std::memcpy
 #include <initializer_list>  // std::initializer_list
 #include <limits>            // std::numeric_limits
-#include <stdexcept>         // std::runtime_error
-#include <string>            // std::string
-#include <system_error>      // std::system_error
+#if defined(__GLIBCXX__) && !defined(_GLIBCXX_USE_DUAL_ABI)
+// Workaround for pre gcc 5 libstdc++.
+#  include <memory>  // std::allocator_traits
+#endif
+#include <stdexcept>     // std::runtime_error
+#include <string>        // std::string
+#include <system_error>  // std::system_error
 
 #include "base.h"
 
@@ -509,14 +513,6 @@ FMT_INLINE void assume(bool condition) {
 #endif
 }
 
-template <typename Allocator, typename Enable = void> struct allocator_size {
-  using type = size_t;
-};
-template <typename Allocator>
-struct allocator_size<Allocator, void_t<typename Allocator::size_type>> {
-  using type = typename Allocator::size_type;
-};
-
 template <typename Char, typename InputIt>
 auto copy_str(InputIt begin, InputIt end, appender out) -> appender {
   get_container(out).append(begin, end);
@@ -915,9 +911,8 @@ class basic_memory_buffer : public detail::buffer<T> {
   static FMT_CONSTEXPR20 void grow(detail::buffer<T>& buf, size_t size) {
     detail::abort_fuzzing_if(size > 5000);
     auto& self = static_cast<basic_memory_buffer&>(buf);
-    constexpr size_t max_size =
-        detail::max_value<typename detail::allocator_size<Allocator>::type>() /
-        sizeof(T);
+    const size_t max_size =
+        std::allocator_traits<Allocator>::max_size(self.alloc_);
     size_t old_capacity = buf.capacity();
     size_t new_capacity = old_capacity + old_capacity / 2;
     if (size > new_capacity)