[PATCH] libio: Implement internal function __libc_readline_unlocked

[Joseph Myers]

On Fri, 6 Jul 2018, Carlos O'Donell wrote:

> We can change GLIBC_PRIVATE symbols at will. There is no stability
> guarantee at all.

With the caveat that GLIBC_PRIVATE interface changes on a release branch 
are dangerous, because they can affect upgrades on live systems (if a 
running process started with old glibc, then there was an upgrade, then 
the running process dlopens a library from the new glibc that depends on a 
change to a GLIBC_PRIVATE interface provided by libc - see the issues when 
some distributions tried to backport the CVE-2014-9761 fix).

-- 
Joseph S. Myers
joseph@codesourcery.com