Since commit 799011bbe7 ("vircrypto: Rely on GnuTLS for hash functions") the
function "gnutls_hash_fast" is used. According to the documentation at
https://www.gnutls.org/manual/html_node/Cryptographic-API.html this function is only
available since version 2.10.0. But m4/virt-gnutls.m4 expects at least 2.2.0. Please
either revert that change, or bump also the required gnutls version.
Olaf