Windows support

[travisdowns]

Support Windows.

Should be straightforward other than the build. I guess we'll use cmake for that.

I don't think libpfc supports Windows but perhaps we can port that too, or else just rely on the default std::chrono based clock.

[travisdowns]

Some pointers to reading perf events in Windows with ETW:

https://twitter.com/pervognsen/status/1270555130706841600 https://gist.github.com/pervognsen/73597a3a732a10922418d62c6c86a427

SO:

https://stackoverflow.com/questions/45428588/can-i-read-the-cpu-performance-counters-from-a-user-mode-program-in-windows

Bruce's blog:

https://randomascii.wordpress.com/2016/11/27/cpu-performance-counters-on-windows/

[travisdowns]

https://twitter.com/SMT_Solvers/status/1413708136704315398

https://gist.github.com/kruxmeier/eb4becb7ba5c16192274f6fce3a47309