Adjust stddef.h to be compatiable with other libc(s)

I faced many issues when compiling libstdC++-V3 and linking against
relibc mainly:
- Missing types (max_align_t)
- Different types definitions(ptrdiff_t , size_t)
- and the fact that wchar_t is part of standard C++ and it seams that we
  canno redefine standard types

include/stddef.h

@@ -4,12 +4,20 @@
 
 #define NULL 0
 
-typedef signed long long ptrdiff_t;
+#ifndef __PTRDIFF_TYPE__
+#define __PTRDIFF_TYPE__ long int
+#endif
+typedef __PTRDIFF_TYPE__ ptrdiff_t;
 
+#ifndef __cplusplus
 typedef int32_t wchar_t;
+#endif /* #ifndef __cplusplus */
 typedef int32_t wint_t;
 
-typedef unsigned long long size_t;
+
+typedef long unsigned int size_t;
+
+typedef struct { long long __ll; long double __ld; } max_align_t;
 
 #define offsetof(type, member) __builtin_offsetof(type, member)