Prepend DESTDIR to CMAKE_INSTALL_PREFIX to run cpack out of the box

[mlaveaux]

I don't know how people ever figured this out in mCRL2, but it seems that pack -G DEB uses a hidden environment variable called DESTDIR to overwrite the CMAKE_INSTALL_PREFIX such that it does not require sudo rights for making the installation package.

With these changes generating the package works properly on Ubuntu and Fedora. This variable does not work on Windows, so this might required special attention that I did not look into. Alternatively, we would have to overwrite CMAKE_INSTALL_PREFIX ourselves in the CI, but this change does seem like the standard "solution".

[trolando]

I had a go at the whole build script with some suggestions from Claude, and the result might actually be cleaner: 1188edd

Can you see if that works for you?

[mlaveaux]

The new version works resolved the cpack issue so this seems to be resolved. By the way I can also open another issue for it, but we get warnings related to this line in the src/CMakeLists.txt of Sylvan:

set_target_properties(sylvan PROPERTIES PUBLIC_HEADER "${SYLVAN_HDRS}")

This yields some warning when running cmake:

$cmake .
CMake Warning (dev) at CMakeLists.txt:190 (install):
  Target sylvan has PUBLIC_HEADER files but no PUBLIC_HEADER DESTINATION.
This warning is for project developers.  Use -Wno-dev to suppress it.

Commenting it out fixes it for us, but just for your information.

[trolando]

Alright! I've fixed that for the next version of Sylvan (or just pull the master branch)