[PATCH] Fix NO_LOCAL_CLIENT_CRED build

[Ray Strode]

Hi,

> Yes, I think so.  Revised patch attached.
> 
> I've tested this a few ways and it seems to be working correctly, but
> it's hard for me to be sure that this is doing the correct thing on all
> targets.

Thanks for working on this! Seems right to me.  My only
comment is I think have_so_peercred could be prefixed with 
xorg_cv_sys_ / AC_CACHE_CHECK could be used to interface with
configure's caching mechanism, but I don't think that really matters.

--Ray