Add support for custom memory allocator to BasicWriter

test/format-impl-test.cc

@@ -46,7 +46,7 @@ TEST(FormatTest, ArgConverter) {
 
 TEST(FormatTest, FormatNegativeNaN) {
   double nan = std::numeric_limits<double>::quiet_NaN();
-  if (getsign(-nan))
+  if (fmt::internal::getsign(-nan))
     EXPECT_EQ("-nan", fmt::format("{}", -nan));
   else
     fmt::print("Warning: compiler doesn't handle negative NaN correctly");