build: force configure failed when perl is missing

build: force configure failed when perl is missing

Perl is necessary to our build processing, it will invoke a lot of
generating script, like: gendispatch.pl. If perl is missing, it's
ok for build from git checkout, because autogen.sh will tell you.
But for compiling from a release tarball, configure will just record
a missing message, and continue, then build failed, like:
https://www.redhat.com/archives/libvirt-users/2014-August/msg00050.html

So need to enhance configure script to handle this negative case.

Reported-by: Hongbin Lu <hongbin@savinetwork.ca>
Signed-off-by: Jincheng Miao <jmiao@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>