Provides SDKs for iOS 14.0 and macOS 10.15.
Mono is patched to fix a regression in Xcode 11.4+, still unfixed by Apple.
Another patch is backported from Unity's Mono fork to fix another issue with
the macOS 11.0 beta SDK.
Fixes missing arguments in Xcode and iOS dockerfiles, seems like some changes
were not properly committed during the last refactor.
The osxcross installation process has been improved and now supports
more recent versions of Xcode than 7, so most of our custom code is
no longer needed.
The xcode packer could also be reworked to use osxcross' SDK packing
script.
Fixes#15.
The previous `['/bin/bash']` was not working, running the image
with `podman run -it <name>` would evaluate to:
```
> sh -c ['/bin/bash']
sh: [/bin/bash]: No such file or directory
```
This saves us from pulling gtk2 and gtk3 as weak deps of
perl and git or whatnot... And we don't need to pull in all
the documentation on Ubuntu.
Also ensures that we properly run `dnf clean all` after each
installation.