Fix clang errors

*** 120,129 ****
--- 120,132 ----
  #endif  /* defined(_XPG6) && !defined(_VA_LIST) */
  
  #ifdef __STDC__
  
  #if !defined(_STRICT_STDC) || defined(_XOPEN_SOURCE) || defined(__EXTENSIONS__)
+ #if __cplusplus >= 199711L
+ namespace std {
+ #endif
  extern int iswalpha(wint_t);
  extern int iswupper(wint_t);
  extern int iswlower(wint_t);
  extern int iswdigit(wint_t);
  extern int iswxdigit(wint_t);
*** 138,147 ****
--- 141,172 ----
  extern wint_t towupper(wint_t);
  extern wchar_t *wcswcs(const wchar_t *, const wchar_t *);
  extern int wcswidth(const wchar_t *, size_t);
  extern int wcwidth(wchar_t);
  extern wctype_t wctype(const char *);
+ #if __cplusplus >= 199711L
+ } /* namespace std */
+ 
+ using std::iswalpha;
+ using std::iswupper;
+ using std::iswlower;
+ using std::iswdigit;
+ using std::iswxdigit;
+ using std::iswalnum;
+ using std::iswspace;
+ using std::iswpunct;
+ using std::iswprint;
+ using std::iswgraph;
+ using std::iswcntrl;
+ using std::iswctype;
+ using std::towlower;
+ using std::towupper;
+ using std::wcswcs;
+ using std::wcswidth;
+ using std::wcwidth;
+ using std::wctype;
+ #endif
  #endif /* !defined(_STRICT_STDC) || defined(_XOPEN_SOURCE)... */
  
  #if defined(__EXTENSIONS__) || \
          (!defined(_STRICT_STDC) && !defined(__XOPEN_OR_POSIX))
          /* || defined(_XPG7) */