Export is_compiled_string and operator""_cf (#4544)

Author: CrackedMatter

include/fmt/compile.h

@@ -15,9 +15,10 @@
 #include "format.h"
 
 FMT_BEGIN_NAMESPACE
+FMT_BEGIN_EXPORT
 
 // A compile-time string which is compiled into fast formatting code.
-FMT_EXPORT class compiled_string {};
+class compiled_string {};
 
 template <typename S>
 struct is_compiled_string : std::is_base_of<compiled_string, S> {};
@@ -59,6 +60,8 @@ template <detail::fixed_string Str> constexpr auto operator""_cf() {
 }  // namespace literals
 #endif
 
+FMT_END_EXPORT
+
 namespace detail {
 
 template <typename T, typename... Tail>