don't define wchar_t on c++

it's a keyword in c++ (wtf). i'm not sure this is the cleanest
solution; it might be better to avoid ever defining __NEED_wchar_t on
c++. but in any case, this works for now.

arch/arm/bits/alltypes.h.sh

@@ -22,7 +22,9 @@ TYPEDEF long ptrdiff_t;
 
 TYPEDEF __builtin_va_list va_list;
 
+#ifndef __cplusplus
 TYPEDEF unsigned wchar_t;
+#endif
 TYPEDEF int wint_t;
 TYPEDEF long wctrans_t;
 TYPEDEF long wctype_t;