crypto: bump min gcrypt to 1.8.0, dropping RHEL-7 support

It has been over two years since RHEL-8 was released, and thus per the
platform build policy, we no longer need to support RHEL-7 as a build
target. This lets us increment the minimum required gcrypt version and
assume that HMAC is always supported

Per repology, current shipping versions are:

             RHEL-8: 1.8.5
      Debian Buster: 1.8.4
 openSUSE Leap 15.2: 1.8.2
   Ubuntu LTS 18.04: 1.8.1
   Ubuntu LTS 20.04: 1.8.5
            FreeBSD: 1.9.2
          Fedora 33: 1.8.6
          Fedora 34: 1.9.3
            OpenBSD: 1.9.3
     macOS HomeBrew: 1.9.3

Ubuntu LTS 18.04 has the oldest version and so 1.8.0 is the new minimum.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210514120415.1368922-6-berrange@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
[thuth: rebased to use .gitlab-ci.d/buildtest.yml]
Signed-off-by: Thomas Huth <thuth@redhat.com>