Merge remote-tracking branch 'remotes/thuth-gitlab/tags/pull-request-2021-07-29'...

Merge remote-tracking branch 'remotes/thuth-gitlab/tags/pull-request-2021-07-29' into staging

* Document GitLab custom CI/CD variables
* Fix 'when:' condition in gitlab-CI jobs
* Disable tests in the gitlab-CI that fail due to out-of-memory conditions
* Allow pushing to "staging" again for maintainers without s390x access
* Fix migration-test build failure on SPARC
* Compile without "pie" on Haiku

# gpg: Signature made Thu 29 Jul 2021 07:17:17 BST
# gpg:                using RSA key 27B88847EEE0250118F3EAB92ED9D774FE702DB5
# gpg:                issuer "thuth@redhat.com"
# gpg: Good signature from "Thomas Huth <th.huth@gmx.de>" [full]
# gpg:                 aka "Thomas Huth <thuth@redhat.com>" [full]
# gpg:                 aka "Thomas Huth <huth@tuxfamily.org>" [full]
# gpg:                 aka "Thomas Huth <th.huth@posteo.de>" [unknown]
# Primary key fingerprint: 27B8 8847 EEE0 2501 18F3  EAB9 2ED9 D774 FE70 2DB5

* remotes/thuth-gitlab/tags/pull-request-2021-07-29:
  configure script fix for Haiku
  tests: Fix migration-test build failure for sparc
  gitlab-ci.d/custom-runners: Improve rules for the staging branch
  gitlab-ci.d/buildtest: Mark the aarch64 and ppc64-s390x CFI jobs as manual
  gitlab-ci.d/buildtest: Disable iotests 197 and 215
  gitlab-ci: Fix 'when:' condition in OpenSBI jobs
  gitlab-ci: Fix 'when:' condition in EDK2 jobs
  gitlab-ci: Fix 'when:' condition in acceptance_test_job_template
  docs: Document GitLab custom CI/CD variables

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>