[libc++] Remove std::function in C++03
`std::function` has been deprecated for a few releases now. Remove it with an option to opt-back-in with a note that this option will be removed in LLVM 16.
Reviewed By: ldionne, #libc
Spies: #libc_vendors, EricWF, jloser, libcxx-commits
Differential Revision: https://reviews.llvm.org/D127908
NOKEYCHECK=True
GitOrigin-RevId: c475e31a189c7ecf181397992875cf526e0d340a
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 2ae3e97..8f4f692 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -148,6 +148,10 @@
will be removed in LLVM 17. You can disable the deprecation warnings by defining
``_LIBCPP_NO_EXPERIMENTAL_DEPRECATION_WARNING_SEARCHERS``.
+- ``std::function`` has been removed in C++03. If you are using it, please remove usages
+ or upgrade to C++11 or later. It is possible to re-enable ``std::function`` in C++03 by defining
+ ``_LIBCPP_ENABLE_CXX03_FUNCTION``. This option it will be removed in LLVM 16.
+
ABI Changes
-----------