[LIBCXX] std::ostream::sentry should be exported

Author: kikairoya

libcxx/include/__ostream/basic_ostream.h

@@ -71,7 +71,7 @@ class basic_ostream : virtual public basic_ios<_CharT, _Traits> {
 
 public:
   // 27.7.2.4 Prefix/suffix:
-  class sentry;
+  class _LIBCPP_EXPORTED_FROM_ABI sentry;
 
   // 27.7.2.6 Formatted output:
   inline _LIBCPP_HIDE_FROM_ABI_AFTER_V1 basic_ostream& operator<<(basic_ostream& (*__pf)(basic_ostream&)) {

libcxx/include/istream

@@ -228,7 +228,7 @@ public:
   basic_istream& operator=(const basic_istream& __rhs) = delete;
 
   // 27.7.1.1.3 Prefix/suffix:
-  class sentry;
+  class _LIBCPP_EXPORTED_FROM_ABI sentry;
 
   // 27.7.1.2 Formatted input:
   inline _LIBCPP_HIDE_FROM_ABI_AFTER_V1 basic_istream& operator>>(basic_istream& (*__pf)(basic_istream&)) {