- Use TIRPC on suse_version >= 1500: sunrpc is deprecated and
should be replaced by TIRPC.

This has several effects:
* We get RPC support back... from build log in oS:F/standard:

[ 48s] checking rpc/types.h usability... no
[ 48s] checking rpc/types.h presence... no
[ 48s] checking for rpc/types.h... no

vs this branch:
[ 50s] checking rpc/types.h usability... yes
[ 50s] checking rpc/types.h presence... yes
[ 50s] checking for rpc/types.h... yes

AND as a side-effect, FALSE for ldapbody.c is now defined (not the
nicest of side-effects, but seems that ldap patch relies on RPC
headers to be included.

So all in all: this fixes the build failures for openSUSE Tumblewee (forwarded request 602971 from dimstar)