Use __GNUC_PATCHLEVEL__ rather than __GNUC_PATCH__, according to the documentation https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html
Eigen is a C++ template library for linear algebra: matrices, vectors, numerical solvers, and related algorithms.
For more information go to http://eigen.tuxfamily.org/.
For pull request, bug reports, and feature requests, go to https://gitlab.com/libeigen/eigen.