fix the type of wchar_t on arm; support wchar_t varying with arch

really wchar_t should never vary, but the ARM EABI defines it as an
unsigned 32-bit int instead of a signed one, and gcc follows this
nonsense. thus, to give a conformant environment, we have to follow
(otherwise L""[0] and L'\0' would be 0U rather than 0, but the
application would be unaware due to a mismatched definition for
WCHAR_MIN and WCHAR_MAX, and Bad Things could happen with respect to
signed/unsigned comparisons, promotions, etc.).

fortunately no rules are imposed by the C standard on the relationship
between wchar_t and wint_t, and WEOF has type wint_t, so we can still
make wint_t always-signed and use -1 for WEOF.

include/wchar.h

@@ -17,6 +17,8 @@ extern "C" {
 
 #include <bits/alltypes.h>
 
+#include <bits/wchar.h>
+
 #undef NULL
 #ifdef __cplusplus
 #define NULL 0
@@ -24,15 +26,9 @@ extern "C" {
 #define NULL ((void*)0)
 #endif
 
-#undef WCHAR_MIN
-#undef WCHAR_MAX
-#define WCHAR_MIN (-1-0x7fffffff)
-#define WCHAR_MAX (0x7fffffff)
-
 #undef WEOF
 #define WEOF (-1)
 
-
 typedef struct
 {
 	unsigned __opaque1, __opaque2;