[libobjc] Fix failures on AIX (PR libobjc/63765)

[Alexandre Oliva]

On Jan 28, 2015, Mike Stump <mikestump@comcast.net> wrote:

> On Jan 28, 2015, at 2:27 AM, Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> wrote:
>> There are two ways to fix this:
>> 
>> * Remove the definition of _XOPEN_SOURCE completely.  This is slightly
>> more risky, but more future-proof since defining features test macros
>> has been an endless source of trouble in the past.

> I think I prefer this one...

> But, as I say that, I read:

>   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=4372

> and there is no hint what host caused him to put the change in, in the
> first place.  :-( Alexandre, do you recall what host needed the
> _XOPEN_SOURCE in libobjc for pthread_mutexattr_settype?

The 2005 timeframe suggests it was probably GNU/Linux, and some digging
in glibc indicates this flag affected nptl's pthread.h's declarations of
various such functions back then.  This changed back in 2010, with glibc
commit d3c7e68655, in response to newer standards, so I guess this
confirms the suggestion from the timeframe.  Of course, this being a
standard-compliance issue, other targets were likely affected as well,
since it looks like there was a standards change, and removing the flag
might cause regressions in old systems that remain stuck to the old
standards.

-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer