mount command: use gethostbyname(3) when building on old systems

mount command: use gethostbyname(3) when building on old	systems

Glibc's getaddrinfo(3) implementation was added over time.  Some old
versions support AI_ADDRCONFIG, but don't define it in header files.
Some older versions don't support AI_ADDRCONFIG at all.

Let's add specific checks to configure.ac to see that the local
getaddrinfo(3) implementation is complete.  If it isn't, we will make
available a resolver that uses gethostbyname(3) and disable IPv6
entirely.

This patch should apply to 1.1.4 as well as the current nfs-utils repo.
The next patch has a fix for the getaddrinfo(3) call added since 1.1.4
in support/nfs/getport.c.

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