[clang] [clang] Define ATOMIC_FLAG_INIT correctly for C++. (PR #97534)

[Chris Copeland via cfe-commits]

https://github.com/chrisnc updated https://github.com/llvm/llvm-project/pull/97534

>From b7857c25e56ea59956d8ae0aac068358bcf67a03 Mon Sep 17 00:00:00 2001
From: Chris Copeland <chris at chrisnc.net>
Date: Wed, 3 Jul 2024 00:11:39 -0700
Subject: [PATCH] [clang] Define ATOMIC_FLAG_INIT correctly for C++.

---
 clang/docs/ReleaseNotes.rst   | 2 ++
 clang/lib/Headers/stdatomic.h | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 1537eaaba0c66..3d85065a7ff8a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -750,6 +750,8 @@ Bug Fixes in This Version
 
 - Fixed `static_cast` to array of unknown bound. Fixes (#GH62863).
 
+- Fixed the definition of ATOMIC_FLAG_INIT in stdatomic.h so it can be used in C++.
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/lib/Headers/stdatomic.h b/clang/lib/Headers/stdatomic.h
index 9c103d98af8c5..51a5d004e82d8 100644
--- a/clang/lib/Headers/stdatomic.h
+++ b/clang/lib/Headers/stdatomic.h
@@ -166,7 +166,11 @@ typedef _Atomic(uintmax_t)          atomic_uintmax_t;
 
 typedef struct atomic_flag { atomic_bool _Value; } atomic_flag;
 
+#ifdef __cplusplus
+#define ATOMIC_FLAG_INIT {false}
+#else
 #define ATOMIC_FLAG_INIT { 0 }
+#endif
 
 /* These should be provided by the libc implementation. */
 #ifdef __cplusplus