Bug 4364

quoting from: http://bugs.debian.org/203412, attached is a patch

===================================================================
SUSv3 [0] states that:

  The following symbolic constant shall be defined only if the
  implementation supports the XSI option; see XSI Conformance.
  
    _XOPEN_VERSION
    [XSI] 
    Integer value indicating version of the X/Open Portability Guide to
        which the implementation conforms. The value shall be 600. 

It furthermore states [0]:

  _XOPEN_UNIX
    [XSI] 
     The implementation supports the XSI extension.

Therefore, if _XOPEN_UNIX is defined, as it is, unconditionally to 1,
then at least at some time _XOPEN_VERSION must be defined to 600.

The only place I can find that _XOPEN_VERSION is mentioned is unistd.h,
which has the following snippet of code:

  /* X/Open version number to which the library conforms.  It is selectable.  
*/
  #ifdef __USE_UNIX98
  # define _XOPEN_VERSION       500
  #else
  # define _XOPEN_VERSION       4
  #endif

There is a complicated set of preprocessor directives in features.h that
chooses appropriately; for _XOPEN_SOURCE=600, _XOPEN_VERSION=500, not
600. Oops.


  [0] http://www.opengroup.org/onlinepubs/007904975/basedefs/unistd.h.html