OK, 11 PM and I think I have all the tests working for Eigen 3.3.3 with all the g++ versions past 4.9 we've been having trouble with. Pull request coming as soon as test-headers passes. I lost all the doc for fvar I added with the last pull req. I'll bring that in later rather than fussing with it now.
Last hurdle was calling
gcc rather than
g++, which works fine until you get to the linker.
@wds15 brought up the issue of whether we'd go past g++ 4.8 support, which is apparently what they have on clusters. No idea how common that is elsewhere. He mentioned that it covers all of C++11 but not all of C++14. No idea how it compares to MSVC.