[libc++] Add tests verifying alphabetical order for several things.

These things are header #includes, CMakeLists.txt, and module.modulemap.

Differential Revision: https://reviews.llvm.org/D116958

NOKEYCHECK=True
GitOrigin-RevId: 42185ad870cb750ede2be38cf5ac5326ab9ac424
diff --git a/include/__debug b/include/__debug
index 4e80474..29c51b2 100644
--- a/include/__debug
+++ b/include/__debug
@@ -23,9 +23,9 @@
 #endif
 
 #if _LIBCPP_DEBUG_LEVEL >= 1 || defined(_LIBCPP_BUILDING_LIBRARY)
-#   include <cstdlib>
-#   include <cstdio>
 #   include <cstddef>
+#   include <cstdio>
+#   include <cstdlib>
 #endif
 
 #if _LIBCPP_DEBUG_LEVEL == 0