https://PR43703 - std::steady_clock::now() frequently overflows on Windows
I'm putting this up for review because I'm not seeing an easy way to test this - and because I don't have a windows box handy.
I tested this patch, and it appears to fix the overflow problem.
(FWIW, I tested using https://gist.github.com/rprichard/bcff3b3fb0451207dc9f31ccbab938df on Wine and on Windows 10. For both targets, the performance counter frequency was 10MHz, so counter.QuadPart * nano::den had previously wrapped around about every 1845 seconds.)