[libc++] Removes a Clang 16 Windows workaround. (#88560)

Author: mordante

libcxx/include/sstream

@@ -330,14 +330,6 @@ typedef basic_stringstream<wchar_t> wstringstream;
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
-// TODO(LLVM-19): Remove this once we drop support for Clang 16,
-// which had this bug: https://github.com/llvm/llvm-project/issues/40363
-#ifdef _WIN32
-#  define _LIBCPP_HIDE_FROM_ABI_SSTREAM _LIBCPP_ALWAYS_INLINE
-#else
-#  define _LIBCPP_HIDE_FROM_ABI_SSTREAM _LIBCPP_HIDE_FROM_ABI
-#endif
-
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 // Class template basic_stringbuf [stringbuf]
@@ -460,9 +452,9 @@ public:
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_BUILDING_LIBRARY)
   string_type str() const;
 #else
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() const& { return str(__str_.get_allocator()); }
+  _LIBCPP_HIDE_FROM_ABI string_type str() const& { return str(__str_.get_allocator()); }
 
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() && {
+  _LIBCPP_HIDE_FROM_ABI string_type str() && {
     const basic_string_view<_CharT, _Traits> __view = view();
     typename string_type::size_type __pos           = __view.empty() ? 0 : __view.data() - __str_.data();
     // In C++23, this is just string_type(std::move(__str_), __pos, __view.size(), __str_.get_allocator());
@@ -948,9 +940,9 @@ public:
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_BUILDING_LIBRARY)
   _LIBCPP_HIDE_FROM_ABI string_type str() const { return __sb_.str(); }
 #else
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() const& { return __sb_.str(); }
+  _LIBCPP_HIDE_FROM_ABI string_type str() const& { return __sb_.str(); }
 
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() && { return std::move(__sb_).str(); }
+  _LIBCPP_HIDE_FROM_ABI string_type str() && { return std::move(__sb_).str(); }
 #endif
 
 #if _LIBCPP_STD_VER >= 20
@@ -1085,9 +1077,9 @@ public:
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_BUILDING_LIBRARY)
   _LIBCPP_HIDE_FROM_ABI string_type str() const { return __sb_.str(); }
 #else
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() const& { return __sb_.str(); }
+  _LIBCPP_HIDE_FROM_ABI string_type str() const& { return __sb_.str(); }
 
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() && { return std::move(__sb_).str(); }
+  _LIBCPP_HIDE_FROM_ABI string_type str() && { return std::move(__sb_).str(); }
 #endif
 
 #if _LIBCPP_STD_VER >= 20
@@ -1225,9 +1217,9 @@ public:
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_BUILDING_LIBRARY)
   _LIBCPP_HIDE_FROM_ABI string_type str() const { return __sb_.str(); }
 #else
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() const& { return __sb_.str(); }
+  _LIBCPP_HIDE_FROM_ABI string_type str() const& { return __sb_.str(); }
 
-  _LIBCPP_HIDE_FROM_ABI_SSTREAM string_type str() && { return std::move(__sb_).str(); }
+  _LIBCPP_HIDE_FROM_ABI string_type str() && { return std::move(__sb_).str(); }
 #endif
 
 #if _LIBCPP_STD_VER >= 20