putchar
=======

POSIX specification:
 http://www.opengroup.org/onlinepubs/9699919799/functions/putchar.html

Gnulib module: stdio, nonblocking, sigpipe

Portability problems fixed by Gnulib module stdio, together with module nonblocking:

  * When writing to a non-blocking pipe whose buffer is full, this function fails with errno being set to ENOSPC instead of EAGAIN on some platforms: mingw.

Portability problems fixed by Gnulib module stdio, together with module sigpipe:

  * When writing to a pipe with no readers, this function fails, instead of obeying the current SIGPIPE handler, on some platforms: mingw.

Portability problems not fixed by Gnulib:

  * On Windows platforms (excluding Cygwin), this function does not set errno upon failure.