[clang] Mention MS on-demand TLS initialization in release notes

[momo5502]

Summary

In change https://reviews.llvm.org/D115456 on-demand TLS initialization for Microsoft CXX ABI was added.

This mentions the change in the release notes.

[hans]

lgtm

[momo5502]

Seems like this can be merged, right?

[hans]

Oh, right. And since the change landed before the branch, this should go on the 14.x release branch. Landed here: https://github.com/llvm/llvm-project/commit/20ea9e379984f240d7135843baae6999abf3bf2b

clang/docs/ReleaseNotes.rst

 ---------------
 
 - An MSVC compatibility workaround for C++ operator names was removed. As a
   result, the ``<query.h>`` Windows SDK header may not compile out of the box.
   Users should use a recent SDK and pass ``-DQUERY_H_RESTRICTION_PERMISSIVE``
   or pass ``/permissive`` to disable C++ operator names altogether. See
   `PR42427 <https://llvm.org/pr42427>` for more info.
 
+- Support for on-demand initialization of TLS variables was added.
+
 C Language Changes in Clang
 ---------------------------
 
 - The value of ``__STDC_VERSION__`` has been bumped to ``202000L`` when passing
   ``-std=c2x`` so that it can be distinguished from C17 mode. This value is
   expected to change again when C23 is published.
 - Wide multi-characters literals such as ``L'ab'`` that would previously be interpreted as ``L'b'``
   are now ill-formed in all language modes. The motivation for this change is outlined in