Merge remote-tracking branch 'remotes/thuth-gitlab/tags/pull-request-2021-09-06' into staging

* Add definitions of terms for CI/testing
* Fix g_setenv problem discovered by Coverity
* Gitlab CI improvements
* Build system improvements (configure script + meson.build)
* Removal of the show-fixed-bugs.sh script
* Clean up of the sdl and curses options

# gpg: Signature made Mon 06 Sep 2021 10:51:49 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-2021-09-06:
  softmmu/vl: Deprecate the -sdl and -curses option
  softmmu/vl: Deprecate the old grab options
  softmmu/vl: Add a "grab-mod" parameter to the -display sdl option
  scripts: Remove the "show-fixed-bugs.sh" file
  configure / meson: Move the GBM handling to meson.build
  meson.build: Don't use internal libfdt if the user requested the system libfdt
  meson.build: Fix the check for a usable libfdt
  gitlab-ci: Don't try to use the system libfdt in the debian job
  libqtest: check for g_setenv() failure
  docs: add definitions of terms for CI/testing

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