Spectre mitigations for msvc

https://blogs.msdn.microsoft.com/vcblog/2018/01/15/spectre-mitigations-in-msvc/

Using LFENCE (recommended by CPU manufacturers).
Anyway, it might have a little (very little) performance drop not likely Google's retpoline.
Check the performance of your application. Depends on the implementations, it could bring a performance drop more than expected.