Unless there is some way to turn off speculation entirely, but that would hurt performance badly.
Spectre is a whole other can of worms, on the one hand it's more tricky to exploit, on the other hand there might not be an easy fix and people are speculating (no pun intended) that it will have to be dealt with in hardware.
Chrome and Firefox are already working on solutions as you cannot exploit the JIT if it generates code that ruins your timing as far as I'm aware.
So that solves the problem for most people, but all other environments that allow execution of untrusted code also need to be updated.