Description of problem:
Manual page for ptsname says it requires '#define _XOPEN_SOURCE' but in fact it requires _XOPEN_SOURCE >= 500.

Version-Release number of selected component (if applicable):
man-pages-4.09-3.fc26.noarch

How reproducible:
Always

Steps to Reproduce:
1. Check manual page
2.
3.

Actual results:
There is written:
      #define _XOPEN_SOURCE       /* See feature_test_macros(7) */
      #include <stdlib.h>

      char *ptsname(int fd);

      #define _GNU_SOURCE         /* See feature_test_macros(7) */
      #include <stdlib.h>

      int ptsname_r(int fd, char *buf, size_t buflen);

Expected results:
In fact it requires:
#define _XOPEN_SOURCE 500

Additional info:
See bug 1520042 for reproducer and details. By consulting feature_test_macros manual page and its example of 'acct' manual page I think the current state is confusing at least.