Fix WCHAR_MAX, WCHAR_MIN, WINT_MAX, and WINT_MIN.

GCC tells us everything we need to know. clang does its usual half-assed job.

Change-Id: Id4d664529b10345274602768cd564d3df717e931

libc/include/wchar.h

@@ -34,7 +34,8 @@
 #include <stdarg.h>
 #include <stddef.h>
 #include <time.h>
-#include <malloc.h>
+
+#include <machine/wchar_limits.h>
 
 __BEGIN_DECLS
 
@@ -58,11 +59,6 @@ typedef enum {
     WC_TYPE_MAX
 } wctype_t;
 
-#ifndef WCHAR_MAX
-#define  WCHAR_MAX   INT_MAX
-#define  WCHAR_MIN   INT_MIN
-#endif
-
 #define  WEOF        ((wint_t)(-1))
 
 extern wint_t            btowc(int);