Specifically:
- Fixed ctz on 32-bit arm (where `uint64_t` is `unsigned long long`)
- Fixed build of random_cpp11 snippet when C++11 is disabled
- Updated CI scripts to run windows on push, and added a no-c++11 test
- Introduce CMake option `EIGEN_SPLIT_TESTSUITE` that allows to divide the single test build target into several subtargets
- Add CI pipeline for merge request that can be run by GitLab's shared runners
- Add nightly CI pipeline