Since commit 4e75b0a00fb4 we support SASL 2.1.26 and newer
releases only, all of which ship a .pc file. Using pkg-config
allows FreeBSD builds to pick up the dependency automatically.
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>