[Bug libfortran/117857] libgfortran on powerpc-darwin8 doesn't compile: `-Wint-conversion` in `stream_ttyname`

[glex.spb at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117857

--- Comment #15 from Gleb Mazovetskiy <glex.spb at gmail dot com> ---
Also in macports, there is only one use of `-D_APPLE_C_SOURCE` in macports, for
the tmux package.

https://github.com/macports/macports-ports/blob/ad9460ffa5b5ff8ce8e7b4e3dd01cf7db07dac8c/sysutils/tmux/Portfile#L80-L83