Fix "undefined reference to `fmt::v7::detail::basic_data<void>::digits'"

Remove unused FMT_EXTERN_TEMPLATE_API

include/fmt/core.h

@@ -253,9 +253,10 @@
 #  endif
 #else
 #  define FMT_CLASS_API
-#  if defined(__GNUC__) || defined(__clang__)
-#    define FMT_API __attribute__((visibility("default")))
-#    define FMT_EXTERN_TEMPLATE_API FMT_API
+#  if defined(FMT_EXPORT) || defined(FMT_SHARED)
+#    if defined(__GNUC__) || defined(__clang__)
+#      define FMT_API __attribute__((visibility("default")))
+#    endif
 #  endif
 #endif
 #ifndef FMT_API

include/fmt/format.h

@@ -902,7 +902,7 @@ template <typename T = void> struct basic_data {
   FMT_API static constexpr const char right_padding_shifts[] = {0, 31, 0, 1, 0};
 };
 
-#ifndef FMT_HEADER_ONLY
+#ifdef FMT_SHARED
 // Required for -flto, -fivisibility=hidden and -shared to work
 extern template struct basic_data<void>;
 #endif