[libcxx-commits] [libcxx] [libc++][modules] Add using_if_exists attribute (#77559) (PR #78909)

[via libcxx-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Gareth Williamson (gwllx)

<details>
<summary>Changes</summary>

libc on macOS does not provide at_quick_exit or quick_exit. This allows modules to build on macOS and defer any errors to usage site of these symbols.

CC: @<!-- -->mordante 

---
Full diff: https://github.com/llvm/llvm-project/pull/78909.diff


1 Files Affected:

- (modified) libcxx/modules/std.compat/cstdlib.inc (+2-2) 


``````````diff
diff --git a/libcxx/modules/std.compat/cstdlib.inc b/libcxx/modules/std.compat/cstdlib.inc
index 9333d848707103..a45a0a1caf8ba9 100644
--- a/libcxx/modules/std.compat/cstdlib.inc
+++ b/libcxx/modules/std.compat/cstdlib.inc
@@ -16,10 +16,10 @@ export {
   // [support.start.term], start and termination
   using ::_Exit;
   using ::abort;
-  using ::at_quick_exit;
+  using ::at_quick_exit _LIBCPP_USING_IF_EXISTS;
   using ::atexit;
   using ::exit;
-  using ::quick_exit;
+  using ::quick_exit _LIBCPP_USING_IF_EXISTS;
 
   using ::getenv;
   using ::system;

``````````

</details>


https://github.com/llvm/llvm-project/pull/78909