dirfd
=====

POSIX specification:
 https://pubs.opengroup.org/onlinepubs/9699919799/functions/dirfd.html

Gnulib module: dirfd

Portability problems fixed by Gnulib:

  * This function is missing on some platforms: Minix 3.1.8, AIX 7.1, HP-UX 11, Solaris 10, mingw, MSVC 14.

Portability problems not fixed by Gnulib:

  * This function always fails on some platforms: mingw.

  * There is a dirfd macro but no function, and the macro does not work with an argument of type void *, as a function would: NetBSD 9.2.