Comment 1 for bug 1669578

Upstream threads: https://sourceware.org/cgi-bin/search.cgi?q=ttyname+and+ttyname_r&cmd=Search%21&form=extended&m=all&ps=10&fmt=long&wm=wrd&sp=1&sy=1&wf=2221&type=&GroupBySite=no&ul=%2Fml%2Flibc-alpha%2F%25

We've been getting about a report a week about things failing due to this bug so we really need it sorted this time (most reports are for screen/tmux and tools that use them like do-release-upgrade).