Description of problem:

Build fails if libtiprc (and libtirpc-devel) are installed on the system, but --with-ipv6-default is not set.

Making all in rpc-lib
Making all in src
  CC       auth-unix.lo
  CC       rpcsvc-auth.lo
  CC       rpcsvc.lo
[...]
rpcsvc.c: In function 'rpcsvc_callback_build_record':
rpcsvc.c:1002:9: error: implicit declaration of function 'xdr_sizeof' [-Werror=implicit-function-declaration]
         xdr_size = xdr_sizeof ((xdrproc_t)xdr_callmsg, &request);
         ^
cc1: some warnings being treated as errors
make[4]: *** [rpcsvc.lo] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [all-recursive] Error 1
make[2]: *** [all-recursive] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2

Version-Release number of selected component (if applicable):

See "Additional info" for the commits causing this.

Additional info:

This error message appeared with https://review.gluster.org/18834, but https://review.gluster.org/18970 mitigated it for the case when --with-ipv6-default is used. However, a libtirpc-but-no-IPv6 build is still not covered.
Note that libtirpc is picked up if present, so no --with-libtirpc option is required to trigger this, only presence of libtirpc{,-devel}.

Workaround: building with "--with-libtirpc=no".

Beyond the mere fix, it could be considered to default to --with-libtirpc=no (unless -with-ipv6-default is used).