[libc++] Fix __threading_support when used with C11 threading

[ldionne]

Since we are defining these typedefs inside namespace std, we need to refer to ::once_flag (the C Standard Library version). Otherwise 'once_flag' refers to 'std::once_flag', and that's not something we can pass to the C Standard Library '::call_once()' function later on.

[llvmbot]

@llvm/pr-subscribers-libcxx

Changes

Since we are defining these typedefs inside namespace std, we need to refer to ::once_flag (the C Standard Library version). Otherwise 'once_flag' refers to 'std::once_flag', and that's not something we can pass to the C Standard Library '::call_once()' function later on.

---

Full diff: https://github.com/llvm/llvm-project/pull/66780.diff

1 Files Affected:

• (modified) libcxx/include/__threading_support (+1-1)

diff --git a/libcxx/include/__threading_support b/libcxx/include/__threading_support
index eaa402abae351b6..ccbcc652d9e50a6 100644
--- a/libcxx/include/__threading_support
+++ b/libcxx/include/__threading_support
@@ -102,7 +102,7 @@ typedef cnd_t __libcpp_condvar_t;
 #define _LIBCPP_CONDVAR_INITIALIZER {}
 
 // Execute once
-typedef once_flag __libcpp_exec_once_flag;
+typedef ::once_flag __libcpp_exec_once_flag;
 #define _LIBCPP_EXEC_ONCE_INITIALIZER ONCE_FLAG_INIT
 
 // Thread id

[ldionne]

I'll ship this since it's a small change that is obviously correct and the CI is happy. This fixes some downstream issues (that's how this patch came about).