Don't make the uninstall target if it already exists

[jmcarcell]

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• Don't make the uninstall target if it already exists

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CMake will throw an error and stop if the uninstall target already exists

[tmadlener]

Is the cmake_uninstall.cmake necessary for anything else or could that be removed as well?

[jmcarcell]

If we remove cmake_uninstall.cmake then ilcsoft_default_uninstall_target.cmake can also be removed; I wasn't proposing that but for me it would be fine since I never make use of the uninstall target.

[tmadlener]

My main concern would be to not have "dead" code around and then having to wonder down the line, whether it can be removed.

Maybe @andresailer or @gaede can shed some light on the use cases of the uninstall target (and how it was used in the past)?

[jmcarcell]

The only useful case that I have found has been when installing to the system in /usr/local, for example, and then when you have multiple packages installed like this uninstalling them is hard since they share installation folders

[tmadlener]

Looking at cmake_uninstall.cmake.in it looks like it pretty much follows what is suggested by cmake:
https://gitlab.kitware.com/cmake/community/-/wikis/FAQ#can-i-do-make-uninstall-with-cmake

So, I think we keep this PR as it is and just guard against a duplicate definition.

[jmcarcell]

Sounds good, iLCSoft/iLCUtil#29 is the same PR