[eigen] Build Matrices

[Patrick Snape <patricksnape@xxxxxxxxx>]

Hi,

We are developing some automated builds for the Python ecosystem over at conda-forge (https://conda-forge.github.io/). In particular, we would like to add an Eigen package (https://github.com/conda-forge/staged-recipes/pull/205). 

I've used Eigen before, but never had to distribute it. Obviously Eigen is header only - however, I know that Eigen does behave differently depending on the compiler used to build a project that relies on it. Therefore, does the CMake Eigen install depend on the compiler? Do we need a build matrix for every Python version that uses the various compilers that match the shipped Python distributions - or do we just need a single build per platform (to put the headers in the correct folder)? 

Thanks for your time,

Patrick