extconf: Print progress message
extconf: Print progress message

This is useful in bug reports to verify that whatever information
has been provided to the build system by the user is actually
being taken into account.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>

libvirt/ruby-libvirt,libvirt/ruby-libvirt,libvirt/ruby-libvirt