[libc++] Alphabetize header inclusions and include-what-you-use <__debug>. NFCI.

NOKEYCHECK=True
GitOrigin-RevId: 06b40e80aefc9a7ccf2efbf7717037bd103a779c
diff --git a/include/numeric b/include/numeric
index 0fd48de..d42cbf9 100644
--- a/include/numeric
+++ b/include/numeric
@@ -145,10 +145,11 @@
 */
 
 #include <__config>
+#include <__debug>
+#include <cmath> // for isnormal
+#include <functional>
 #include <iterator>
 #include <limits> // for numeric_limits
-#include <functional>
-#include <cmath> // for isnormal
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)