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

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

NOKEYCHECK=True
GitOrigin-RevId: bfbd73f87d7b2c1140b43192cea6b7fbbfc35cd0
diff --git a/include/variant b/include/variant
index 426683a..5a431c3 100644
--- a/include/variant
+++ b/include/variant
@@ -199,19 +199,19 @@
 
 */
 
-#include <__config>
 #include <__availability>
+#include <__config>
 #include <__tuple>
 #include <array>
 #include <compare>
 #include <exception>
 #include <functional>
 #include <initializer_list>
+#include <limits>
 #include <new>
 #include <tuple>
 #include <type_traits>
 #include <utility>
-#include <limits>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)