Kernel+LibC: Move errno definitions to Kernel/API/POSIX

This fixes at least half of our LibC includes in the kernel. The source
of truth for errno codes and their description strings now lives in
Kernel/API/POSIX/errno.h as an enumeration, which LibC includes.

Userland/Utilities/syscall.cpp

@@ -9,7 +9,7 @@
 #include <AK/Iterator.h>
 #include <AK/Vector.h>
 #include <LibCore/ArgsParser.h>
-#include <errno_numbers.h>
+#include <errno_codes.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>