CMake find module

[jenskeiner]

Transferred from: https://github.com/NFFT/nfft_old/issues/12

I wrote a CMake find module to help the discovery of the different components of NFFT v3.3 inside projects using CMake as their build system. Would you guys be interested to have it upstream in the repository ?

[kevinmatthes]

In my opinion, it is definitely an interesting feature to have an alternative build system in case that the current one, automake, should not be available for some reasons on some machines.

I would like to suggest to think about an integration for the next bigger release in order to enhance the portability to different systems. For testing and debugging, we could bind it as a submodule from an external repository within the NFFT namespace such that we can adjust it easier without too much overhead to this repository.

Which version of cmake does the suggested build routine require, at the moment? Does it work with the latest versions (for instance version 3.20.x or newer), too, or does it require a certain older version?

[kevinmatthes]

When we would outsource both build routines to different repositories within the NFFT namespace -- and bind both as submodules --, users could decide for one during the cloning process (by just cloning the preferred one) or, in a later step, by passing an option to bootstrap.sh or configure in order to proceed with the selected build system.

Thereby, we would be more flexible regarding adjustments of the build system since we would have a fallback solution -- the opposite build system -- in case that an update to one of the systems would cause problems. Hence, the project could be developed more flexible since the build routines could be updated one after another.