mount: getport: don't use getaddrinfo(3) on old systems

Older glibc versions have a getaddrinfo(3) that doesn't support
AI_ADDRCONFIG.  Detect that case and build something else for
getport.c that will work adequately on those systems.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>