[libcxx] Make the visibility attributes consistent for __narrow_to_utf8/__widen_from_utf8

[mstorsjo]

Summary

Use the same visiblity attributes as for all other template
specializations in the same file; declare the specialization itself
using _LIBCPP_TYPE_VIS, and don't use _LIBCPP_EXPORTED_FROM_ABI on
the destructor. Methods that are excluded from the ABI are marked
with _LIBCPP_INLINE_VISIBILITY.

This makes the vtable exported from DLL builds of libc++. Practically,
it doesn't make any difference for the CI configuration, but it
can make a difference in mingw setups.

[mstorsjo]

Ping

libcxx/include/__locale

operator()(_OutputIterator __s, const _CharT* __wb, const _CharT* __we) const
         for (; __wb < __we; ++__wb, ++__s)
             *__s = *__wb;
         return __s;
     }
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
 template <>
-struct _LIBCPP_TEMPLATE_VIS __narrow_to_utf8<16>
+struct _LIBCPP_TYPE_VIS __narrow_to_utf8<16>
     : public codecvt<char16_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __narrow_to_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    _LIBCPP_EXPORTED_FROM_ABI ~__narrow_to_utf8();
+    ~__narrow_to_utf8();
 
     template <class _OutputIterator, class _CharT>
     _LIBCPP_INLINE_VISIBILITY
     _OutputIterator
     operator()(_OutputIterator __s, const _CharT* __wb, const _CharT* __we) const
     {
         result __r = ok;
         mbstate_t __mb;
operator()(_OutputIterator __s, const _CharT* __wb, const _CharT* __we) const
             __wb = (const _CharT*)__wn;
         }
         return __s;
     }
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
 template <>
-struct _LIBCPP_TEMPLATE_VIS __narrow_to_utf8<32>
+struct _LIBCPP_TYPE_VIS __narrow_to_utf8<32>
     : public codecvt<char32_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __narrow_to_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    _LIBCPP_EXPORTED_FROM_ABI ~__narrow_to_utf8();
+    ~__narrow_to_utf8();
 
     template <class _OutputIterator, class _CharT>
     _LIBCPP_INLINE_VISIBILITY
     _OutputIterator
     operator()(_OutputIterator __s, const _CharT* __wb, const _CharT* __we) const
     {
         result __r = ok;
         mbstate_t __mb;
operator()(_OutputIterator __s, const char* __nb, const char* __ne) const
         for (; __nb < __ne; ++__nb, ++__s)
             *__s = *__nb;
         return __s;
     }
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
 template <>
-struct _LIBCPP_TEMPLATE_VIS __widen_from_utf8<16>
+struct _LIBCPP_TYPE_VIS __widen_from_utf8<16>
     : public codecvt<char16_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __widen_from_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    _LIBCPP_EXPORTED_FROM_ABI ~__widen_from_utf8();
+    ~__widen_from_utf8();
 
     template <class _OutputIterator>
     _LIBCPP_INLINE_VISIBILITY
     _OutputIterator
     operator()(_OutputIterator __s, const char* __nb, const char* __ne) const
     {
         result __r = ok;
         mbstate_t __mb;
operator()(_OutputIterator __s, const char* __nb, const char* __ne) const
             __nb = __nn;
         }
         return __s;
     }
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
 template <>
-struct _LIBCPP_TEMPLATE_VIS __widen_from_utf8<32>
+struct _LIBCPP_TYPE_VIS __widen_from_utf8<32>
     : public codecvt<char32_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __widen_from_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    _LIBCPP_EXPORTED_FROM_ABI ~__widen_from_utf8();
+    ~__widen_from_utf8();
 
     template <class _OutputIterator>
     _LIBCPP_INLINE_VISIBILITY
     _OutputIterator
     operator()(_OutputIterator __s, const char* __nb, const char* __ne) const
     {
         result __r = ok;
         mbstate_t __mb;