[RFC] want to #undef HAVE_SBRK and HAVE_POLL on Interix

[Joel Brobecker <brobecker at gnat dot com>]

Hello,

This is something I did sometime ago, and wanted to discuss with you
before proposing a change more formally. 

Here goes: On Interix, the sbrk() function exists, but is not
sufficiently implemented to be used in GDB. Because it exists,
AC_CHECK_FUNCS (sbrk) finds it, and therefore configure adds the
associated "#define HAVE_SBRK" in config.h.

If you look at xm-interix.h in the files I recently submitted, you will
see that there is a "#undef HAVE_SBRK" to counter the result of
AC_CHECK_FUNCS. I would like to get rid of this #undef. To do that, the
only way I found is to either:
  1. let configure test for sbrk() on Interix, but then override the
     test result afterward by undefining (in the configure sense)
     HAVE_SBRK. Something like:

     AC_CHECK_FUNCS (....)     # this line is unchanged
     case "${host}" in
       *-*-interix* )
         undefine (HAVE_BRK)
         ;;
       * )
         ;;
     esac
     
  2. do not do the AC_CHECK_FUNCS test for sbrk() on Interix. This way,
     HAVE_SBRK will never be defined, and we don't need the undef in
     xm-interix.h anymore.

I did not find a way in the documentation to undefine a variable that
was previously defined. So I could not implement 1. I also thought that
a user might find it confusing to see the output of configure show

     Checking for sbrk... yes

and then no see HAVE_SBRK defined in config.h...
     
So I implemented 2. A patch is attached (it is only the configure.in
part, the rest will follow if the approach to the problem is approved).
I also did the same for the poll() function, which should not be used
on Interix as well.

Is it the best approach to the problem? Would such a patch be accepted
for inclusion?

Thanks,
-- 
Joel

Attachment: configure.in.diff2
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