Remove redundant wchar_t and win_t definitions

Typically with libc implementations, wchar_t and co are either defined
entirely by the libc or, under libc's arrangement, by headers supplied
by the compiler.

Things like dlmalloc in relibc need these definitions from relibc itself
and that's already already furnished by relibc's stddef.h.

These additional definitions here are redundant and collide with
compiler headers - for example: onig_sys (something that uutils depends
on) breaks. Instead, this patch makes the compiler headers define
things appropriately.

include/bits/wchar.h

@@ -6,7 +6,9 @@
 #define WCHAR_MIN (0)
 #define WCHAR_MAX (0x7fffffff)
 
-typedef int32_t wchar_t;
-typedef uint32_t wint_t;
+#define __need_size_t
+#define __need_wchar_t
+#define __need_wint_t
+#define __need_NULL
 
 #endif /* _BITS_WCHAR_H */