Install xz/xz-utils and conditionally handle tar.xz tarballs from 6.0+.
On Windows, I ran into a build issue due to `make distclean` being
bogus in 6.0.0.319 (mono/mono#16605), so I worked it around by starting
from a clean folder for each build.
The hotfixed mingw-binutils packages should likely be rebuilt against
Fedora 30's mingw-binutils, but I didn't find the src.rpm in the repo
to do it. There were no functional changes between F29 and F30's
mingw-binutils though, so we should be fine as is:
https://src.fedoraproject.org/rpms/mingw-binutils/commits/f30
The `MONO32_PREFIX` and `MONO64_PREFIX` are no longer used by the
buildsystem (replaced by a `mono_prefix` build option), but I kept them
where relevant to point to non-standard install locations.
* Mono config on MacOSX is not portable from the Linux and Windows
version.
* Rename the compilers so that 'gcc' and 'g++' are the new version by
default.
* Add default environment variables to containers.
Rémi Verschelde
Hein-Pieter van Braam