If the Sun guy only commented on _XOPEN_SOURCE_EXTENDED, I'm not sure
that this also applies to _XOPEN_SOURCE. For example, on my Solaris 9,
I have (in signal.h) conditionally

#pragma redefine_extname sigwait __posix_sigwait 

and in sys/socket.h

#pragma redefine_extname connect __xnet_connect

So these feature selection macros not only select what API is declared
in the header files, but also what specific semantics some of the
functions have (e.g. if the traditional BSD semantics deviates from the
POSIX semantics).

In cases where there are alternative implementations of some system
calls, we *want* to select the POSIX definition. So I think we should
continue to define _XOPEN_SOURCE. I don't mind also defining __EXTENSIONS__.