Thread safety fixes.

*** 113,122 ****
--- 113,123 ----
  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 */