[clang] [KeyInstr] Add release note following #149509 (PR #156005)

[Orlando Cazalet-Hyams via cfe-commits]

https://github.com/OCHyams created https://github.com/llvm/llvm-project/pull/156005

Key Instructions (-gkey-instructions) is now enabled by default when DWARF is
being emitted, the input is plain C/C++, and optimisations are enabled.

Add release note for the change in default behaviour.

>From d53c1b3964064d1a57dc0b588a636197959cdaf7 Mon Sep 17 00:00:00 2001
From: Orlando Cazalet-Hyams <orlando.hyams at sony.com>
Date: Fri, 29 Aug 2025 11:46:50 +0100
Subject: [PATCH] [KeyInstr] Add release note following #149509

Key Instructions (-gkey-instructions) is now enabled by default when DWARF is
being emitted, the input is plain C/C++, and optimisations are enabled.

Add release note for the change in default behaviour.
---
 clang/docs/ReleaseNotes.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 06cc31f8c5c97..739fd50179d25 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -211,6 +211,7 @@ Deprecated Compiler Flags
 
 Modified Compiler Flags
 -----------------------
+- The `-gkey-instructions` compiler flag is now enabled by default when DWARF is emitted for plain C/C++ and optimizations are enabled. (#GH149509)
 
 Removed Compiler Flags
 -------------------------