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

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

NOKEYCHECK=True
GitOrigin-RevId: bfbd73f87d7b2c1140b43192cea6b7fbbfc35cd0
diff --git a/include/fstream b/include/fstream
index dd1aa72..09af0d9 100644
--- a/include/fstream
+++ b/include/fstream
@@ -179,8 +179,8 @@
 
 */
 
-#include <__config>
 #include <__availability>
+#include <__config>
 #include <__debug>
 #include <__locale>
 #include <cstdio>