unistd.h and sleep() are normally Unix-specific, although mingw also provides them.
The Windows C runtime documents _environ as its equivalent of Unix environ.
https://bugs.freedesktop.org/show_bug.cgi?id=90089
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
This is installed by default, but easy to filter out for embedded systems
or whatever.
Based on earlier work by Simon McVittie and Will Thompson
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=34140
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>