[Python-Dev] _XOPEN_SOURCE on Solaris

["Martin v. Löwis"]

In issue 1759169 people have been demanding for quite some time that the 
definition of _XOPEN_SOURCE on Solaris should be dropped, as it was 
unneeded and caused problems for other software.

Now, issue 8864 reports that the multiprocessing module fails to 
compile, and indeed, if _XOPEN_SOURCE is not defined, control messages 
stop working. Several of the CMSG interfaces are only available if 
_XPG4_2 is defined (and, AFAICT, under no other condition); this, in 
turn, apparently is only defined if _XOPEN_SOURCE is 500, 600, or (has 
an arbitrary value and _XOPEN_SOURCE_EXTENDED is 1).

So how should I go about fixing that?
a) revert the patch for #1759169, documentating that Python compilation
    actually requires _XOPEN_SOURCE to be defined, or
b) define _XOPEN_SOURCE only for the multiprocessing module.

Any input appreciated.

Regards,
Martin