[SDK] Reorganize header files

SDK/INC/CRT/stddef.h

@@ -0,0 +1,60 @@
+/*++
+
+Copyright (c) 2024, Quinn Stephens.
+Provided under the BSD 3-Clause license.
+
+Module Name:
+
+   stddef.h
+
+Abstract:
+
+   Provides standard types and definitions.
+
+--*/
+
+#pragma once
+
+#ifndef _STDDEF_H
+#define _STDDEF_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef NULL
+#ifdef __cplusplus
+#define NULL 0
+#else
+#define NULL ((void*)0)
+#endif
+#endif
+
+#ifndef _SIZE_T_DEFINED
+#define _SIZE_T_DEFINED
+#ifdef _WIN64
+typedef unsigned __int64 size_t;
+#else
+typedef unsigned int size_t;
+#endif
+#endif
+
+#ifndef _PTRDIFF_T_DEFINED
+#define _PTRDIFF_T_DEFINED
+#ifdef _WIN64
+typedef __int64 ptrdiff_t;
+#else
+typedef long int ptrdiff_t;
+#endif
+#endif
+
+#ifndef _WCHAR_T_DEFINED
+#define _WCHAR_T_DEFINED
+typedef unsigned short wchar_t;
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* !_STDDEF_H */