libluna+kernel: Move luna/Syscall.h to the kernel API directory

A kernel-specific header has nothing to do in libluna.

apps/sysfuzz.cpp

@@ -1,4 +1,4 @@
-#include <luna/Syscall.h>
+#include <moon/Syscall.h>
 #include <os/ArgumentParser.h>
 #include <stdio.h>
 #include <stdlib.h>

kernel/src/sys/Syscall.h

@@ -1,7 +1,7 @@
 #pragma once
+#include "api/Syscall.h"
 #include "arch/CPU.h"
 #include <luna/Result.h>
-#include <luna/Syscall.h>
 
 typedef u64 SyscallArgs[6];
 

libc/include/sys/syscall.h

@@ -3,8 +3,8 @@
 #ifndef _SYS_SYSCALL_H
 #define _SYS_SYSCALL_H
 
-/* This header just forwards to luna/Syscall.h, which is used in the kernel as well. */
-#include <luna/Syscall.h>
+/* This header just forwards to the kernel API header Syscall.h. */
+#include <moon/Syscall.h>
 #undef enumerate_syscalls
 
 #endif