fix build failure introduced by 5.1-marvel merge

include/m_ctype.h:
  update prototype to reflect changes to my_strchr.c

include/m_ctype.h

@@ -446,7 +446,7 @@ int my_wildcmp_unicode(CHARSET_INFO *cs,
 extern my_bool my_parse_charset_xml(const char *bug, uint len,
 				    int (*add)(CHARSET_INFO *cs));
 extern char *my_strchr(CHARSET_INFO *cs, const char *str, const char *end,
-                       char c);
+                       pchar c);
 
 my_bool my_propagate_simple(CHARSET_INFO *cs, const uchar *str, uint len);
 my_bool my_propagate_complex(CHARSET_INFO *cs, const uchar *str, uint len);