bug#17773: AIX build errors with coreutils-8.22

[Paul Eggert]

Pádraig Brady wrote:

> threading primitives will be used in the regex replacement _if_
> your package is using threads, i.e. has referenced the threadlib gnulib module.

Unfortunately regex also uses threads if the pthread module is used, and 
that's the problem here.  Some coreutils commands ('sort') use threads 
and others don't, but the commands that use threads are careful to not 
invoke anything like stdio or regex in an area where it wouldn't be 
thread-safe.  So I installed the attached hack instead: it abuses 
unlocked-io to mean "unlocked everything" but seemed simpler than 
anything else I could think of.  It fixes the reported problem on AIX 
anyway.

> Paul I see in the threadlib module, the addition of _REENTRANT
> or _THREAD_SAFE defines on some platforms.
> Should we be doing that also in the pthread module?

We do have a problem here.  Won't defining _THREAD_SAFE run into 
problems when combined with unlocked-io on AIX?

To be honest, the unlocked-io stuff seems so quaint now.  How much does 
it really help performance?  Perhaps we should retire it, or turn it 
into a no-op?

0001-regex-don-t-be-multithreaded-if-USE_UNLOCKED_IO.patch
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