[libcxx] Implement P0883R2 ("Fixing Atomic Initialization")

Reviewed By: Quuxplusone

Differential Revision: https://reviews.llvm.org/D103769

NOKEYCHECK=True
GitOrigin-RevId: 56aac567acfd696f54163e33d8df02dc2ad3a72e
diff --git a/include/version b/include/version
index 3d1554b..a0ec730 100644
--- a/include/version
+++ b/include/version
@@ -283,7 +283,7 @@
 // #   define __cpp_lib_atomic_shared_ptr                  201711L
 # endif
 # if !defined(_LIBCPP_HAS_NO_THREADS)
-// #   define __cpp_lib_atomic_value_initialization        201911L
+#   define __cpp_lib_atomic_value_initialization        201911L
 # endif
 # if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_atomic_wait)
 #   define __cpp_lib_atomic_wait                        201907L