[llvm-branch-commits] [clang] release/18.x: [Headers] Don't declare unreachable() from stddef.h in C++ (#86748) (PR #87696)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-x86

@llvm/pr-subscribers-clang

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport df69a305253f1d1b4a4066055a07101a4cc03e55

Requested by: @<!-- -->ian-twilightcoder

---
Full diff: https://github.com/llvm/llvm-project/pull/87696.diff


1 Files Affected:

- (modified) clang/lib/Headers/__stddef_unreachable.h (+4) 


``````````diff
diff --git a/clang/lib/Headers/__stddef_unreachable.h b/clang/lib/Headers/__stddef_unreachable.h
index 518580c92d3f5d..61df43e9732f8a 100644
--- a/clang/lib/Headers/__stddef_unreachable.h
+++ b/clang/lib/Headers/__stddef_unreachable.h
@@ -7,6 +7,8 @@
  *===-----------------------------------------------------------------------===
  */
 
+#ifndef __cplusplus
+
 /*
  * When -fbuiltin-headers-in-system-modules is set this is a non-modular header
  * and needs to behave as if it was textual.
@@ -15,3 +17,5 @@
     (__has_feature(modules) && !__building_module(_Builtin_stddef))
 #define unreachable() __builtin_unreachable()
 #endif
+
+#endif

``````````

</details>


https://github.com/llvm/llvm-project/pull/87696