Thread safety fixes.

@@ -113,10 +113,11 @@
 extern  int isspecial(wint_t);
 /* From BSD/MacOS */
 extern  int iswideogram(wint_t);
 extern  int iswphonogram(wint_t);
 extern  int iswnumber(wint_t);
+extern  int iswhexnumber(wint_t);
 extern  int iswspecial(wint_t);
 
 #else   /* __STDC__ */
 
 /* is* also become functions */