Fix clang errors

@@ -120,10 +120,13 @@
 #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);

@@ -138,10 +141,32 @@
 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) */