* docker/Dockerfile_opensuse-leap_15.3: The 'opensuse/leap:15.3'
docker image doesn't seem to have gcc11, so use gcc10 instead.
* packaging/rules/rpm/jami-gnome.spec: Unconditionally require
'make' for build, and require 'cmake' only where a recent enough
version is available in the distro (otherwise, we grab and use
external cmake e.g. using 'scripts/install-cmake.sh').

jami-packaging#111


Co-authored-by: Amin Bandali <amin.bandali@savoirfairelinux.com>
Change-Id: I5686f8e5d77eb8108b1581a33a2432006a1a688b