[Bug libstdc++/54847] --enable-libstdcxx-time=yes non-functional on darwin

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54847

--- Comment #29 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-10-08 14:32:42 UTC ---
(In reply to comment #28)
> It seems like there is only two possible patches here using the existing
> infrastructure in acinclude.m4 that would allow darwin's nanosleep() to be
> found when passing --enable-libstdcxx-time=yes. Either...
> 
> Index: acinclude.m4
> ===================================================================
> --- acinclude.m4    (revision 192206)
> +++ acinclude.m4    (working copy)
> @@ -1249,7 +1249,7 @@ AC_DEFUN([GLIBCXX_ENABLE_LIBSTDCXX_TIME]
>      [#include <unistd.h>
>       #include <time.h>
>      ],
> -    [#if _POSIX_TIMERS > 0
> +    [#if _POSIX_TIMERS != 0

This is just wrong.

See
http://pubs.opengroup.org/onlinepubs/009695399/basedefs/unistd.h.html#tag_13_80_03_02
for the meaning of the values.

_POSIX_TIMERS=200112L would mean darwin provides a pre-2008 nanosleep, -1 means
the Timers option is not supported.

> Or are you going to demand that the use of pre-2008 POSIX nanosleep() be only
> accepted on a target-specific basis?

There are plenty of systems with a 2001 nanosleep that define _POSIX_TIMERS to
20112L, but darwin seems to support nanosleep without the rest of the Timers
option.  I don't want to remove the correct check for _POSIX_TIMERS just for
one system's peculiarities.