OK, that’s a very similar CPU to mine, it’s 64-bit, and has all the SSE4 extensions. MRtrix3 is compiled for a 64-bit architecture, everything seems to check out OK.
So the only thing I can think of now is that there might be a bug in the particular version of Eigen that you’re running: this is actually not their stable release version, but looks to me like their 3.3 beta. @NicholasDowson also reported issues compiling on 16.04 against that version of Eigen, and reverted back to the release version to build successfully. We issued a fix to compile on that version of Eigen only yesterday… But while it fixes the compilation issue, no one has actually verified that things worked properly with that version of Eigen…
So maybe your simplest bet is to follow the instructions we’d provided to use the stable release version of Eigen, see if that fixes the problem…