C++11 and C++14 require static constexpr data members to have an explicit definition, however master has moved on to C++17 (which deprecates this), and most instances seem to build fine in practice (perhaps only with optimisations enabled?). The only time I have seen it cause a build failure, is with the new Speedy Trial activation code, and fixing the affected variables there would be trivial in comparison to fixing them throughout the whole codebase. So I'm not sure if it's worth the effort to fix this for 0.20/0.21.
C++11 and C++14 require static constexpr data members to have an explicit definition, however master has moved on to C++17 (which deprecates this), and most instances seem to build fine in practice (perhaps only with optimisations enabled?). The only time I have seen it cause a build failure, is with the new Speedy Trial activation code, and fixing the affected variables there would be trivial in comparison to fixing them throughout the whole codebase. So I'm not sure if it's worth the effort to fix this for 0.20/0.21.