[clang] Revert "[Docs] Add release note about Clang-defined target OS macros … (PR #80045)

[Zixu Wang via cfe-commits]

https://github.com/zixu-w updated https://github.com/llvm/llvm-project/pull/80045

>From a38fe65d4ae26bae827d66009ae57236de597055 Mon Sep 17 00:00:00 2001
From: Zixu Wang <zixu_wang at apple.com>
Date: Tue, 30 Jan 2024 10:44:21 -0800
Subject: [PATCH] Revert "[Docs] Add release note about Clang-defined target OS
 macros (#79879)"

This reverts commit b40d5b1b08564d23d5e0769892ebbc32447b2987.

The target OS macros work is included in the 18.x release. Move the
release note to the release branch.
---
 clang/docs/ReleaseNotes.rst | 26 --------------------------
 1 file changed, 26 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ef2d9b8e46ae4e..bac166e6c35627 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -62,21 +62,6 @@ Clang Frontend Potentially Breaking Changes
   of ``-Wno-gnu-binary-literal`` will no longer silence this pedantic warning,
   which may break existing uses with ``-Werror``.
 
-Target OS macros extension
-^^^^^^^^^^^^^^^^^^^^^^^^^^
-A new Clang extension (see :ref:`here <target_os_detail>`) is enabled for
-Darwin (Apple platform) targets. Clang now defines ``TARGET_OS_*`` macros for
-these targets, which could break existing code bases with improper checks for
-the ``TARGET_OS_`` macros. For example, existing checks might fail to include
-the ``TargetConditionals.h`` header from Apple SDKs and therefore leaving the
-macros undefined and guarded code unexercised.
-
-Affected code should be checked to see if it's still intended for the specific
-target and fixed accordingly.
-
-The extension can be turned off by the option ``-fno-define-target-os-macros``
-as a workaround.
-
 What's New in Clang |release|?
 ==============================
 Some of the major new features and improvements to Clang are listed
@@ -161,17 +146,6 @@ Non-comprehensive list of changes in this release
 New Compiler Flags
 ------------------
 
-.. _target_os_detail:
-
-Target OS macros extension
-^^^^^^^^^^^^^^^^^^^^^^^^^^
-A pair of new flags ``-fdefine-target-os-macros`` and
-``-fno-define-target-os-macros`` has been added to Clang to enable/disable the
-extension to provide built-in definitions of a list of ``TARGET_OS_*`` macros
-based on the target triple.
-
-The extension is enabled by default for Darwin (Apple platform) targets.
-
 Deprecated Compiler Flags
 -------------------------