[libc++] Alphabetize and include-what-you-use. NFCI.

Differential Revision: https://reviews.llvm.org/D102781

NOKEYCHECK=True
GitOrigin-RevId: bfbd73f87d7b2c1140b43192cea6b7fbbfc35cd0
diff --git a/include/atomic b/include/atomic
index 5ab10da..2f47f6b 100644
--- a/include/atomic
+++ b/include/atomic
@@ -574,8 +574,8 @@
 
 */
 
-#include <__config>
 #include <__availability>
+#include <__config>
 #include <__threading_support>
 #include <cstddef>
 #include <cstdint>