tests: perform cross compiler builds on GitLab CI

GitLab CI provides some shared build runners that use Docker containers.
This resource can usefully run cross-compiled builds since all other CI
build testing is currently x86 only, and Travis CI is already very busy
testing native builds.
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

.gitlab-ci.yml

+.job_template: &job_definition
+  script:
+    - mkdir build
+    - cd build
+    - ../autogen.sh $CONFIGURE_OPTS || (cat config.log && exit 1)
+    - make -j $(getconf _NPROCESSORS_ONLN)
+
+# We could run every arch on both versions, but it is a little
+# overkill. Instead we run half the jobs on 9 and half the jobs
+# on sid to give reasonable cross-coverage.
+
+debian-9-cross-armv6l:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-9-cross-armv6l:master
+
+debian-9-cross-mipsel:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-9-cross-mipsel:master
+
+debian-9-cross-ppc64le:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-9-cross-ppc64le:master
+
+debian-9-cross-s390x:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-9-cross-s390x:master
+
+debian-sid-cross-aarch64:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-sid-cross-aarch64:master
+
+debian-sid-cross-armv7l:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-sid-cross-armv7l:master
+
+debian-sid-cross-i686:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-sid-cross-i686:master
+
+debian-sid-cross-mips64el:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-sid-cross-mips64el:master
+
+debian-sid-cross-mips:
+  <<: *job_definition
+  image: quay.io/libvirt/buildenv-debian-sid-cross-mips:master