[libc++] Implement `thread::id` comparators as free functions
So far, the `thread::id` comparators were implemented as hidden friends.
This was non-conforming and lead to incorrectly rejected C++ code, as
can be seen in the linked Github issue.
Fixes https://github.com/llvm/llvm-project/issues/56187
Differential Revision: https://reviews.llvm.org/D131430
NOKEYCHECK=True
GitOrigin-RevId: 2d34cb74b5257ecddfb5781c413232f4ecf99016
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index e8f1f9d..9eed868 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -48,6 +48,12 @@
Upcoming Deprecations and Removals
----------------------------------
+API Changes
+-----------
+- The comparison operators on ``thread::id`` are now defined as free-standing
+ functions instead of as hidden friends, in conformance with the C++ standard.
+ Also see `issue 56187 <https://github.com/llvm/llvm-project/issues/56187>`_.
+
ABI Affecting Changes
---------------------