[Cin] AppImage for aarc64

[mnieuw at zap.a2000.nl]

Just now I manage to build a working CinGg AppImage for aarch64, based
in CinGG 2022-02 with the deflate disable for tiff.

To build an AppImage, you need three steps:
- Build an AppDir with the CinGG code in it.
- Then linuxdeploy figures out what more is needed, like system
  libraries. It copies those in the AppDir, then patches all ELF files
  to cater for non-standard locations. Patchelf is not part of
  linuxdeploy, it takes the one from the system, at least for the
  dynamic built linuxdeploy.
- Then the "appimagetool" is run on the AppDir, which makes the actual
  AppImage. This tool is available for 64 and 32 bit, on x86 and arm.

The main problem was linuxdeploy, which is not available for aarch64.

Linuxdeploy does not build straight out of github for me, at least not
so far. It uses cmake (unfamiliar for me).
So I vandalised it a bit, now it builds. I did not try to build the
appimagetool plugin, because that is available as a separate tool.
So this linuxdeploy at the moment is not a full replacement for the
standard linuxdeploy appimage, but that was not a priority.

With these two and a small mode to bld_appimahe.sh, creation of the
CinGG AppImage works fine.

Next is to clean up and document things, so others can reproduce it at
will.
Also, it would be nice to convert linuxdeploy (and appimagetool) to
autotools, if that succeeds then it can be fully integrated in CinGG
(like the thirdparty things are).