[SDK] Big update

Signed-off-by: Quinn Stephens <quinn@osmora.org>

SDK/INC/CRT/stddef.h

@@ -1,6 +1,6 @@
 /*++
 
-Copyright (c) 2024, Quinn Stephens.
+Copyright (c) 2024-2025, Quinn Stephens.
 Provided under the BSD 3-Clause license.
 
 Module Name:
@@ -16,14 +16,16 @@ Abstract:
 #pragma once
 
 #ifndef _STDDEF_H
-#define _STDDEF_H
+#define _STDDEF_H 1
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 #ifndef NULL
-#ifdef __cplusplus
+#if defined(__cplusplus) && __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
 #define NULL 0
 #else
 #define NULL ((void*)0)