isatty
======

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

Gnulib module: isatty

Portability problems fixed by Gnulib:

  * This function is declared in a different header file (namely, <io.h>) on some platforms: MSVC 14.

  * On native Windows, this function also returns true for character devices such as NUL.

  * On native Windows, this function returns false for Cygwin consoles.

  * This function crashes when invoked with invalid arguments on some platforms: MSVC 14.

Portability problems not fixed by Gnulib: