There are two completely unrelated issues being discussed. The only commonality is: yet more annoying Intel CPU security worries.
The topic title is a bit misleading.
1. Meltdown and Spectre - so old that it would be surprising if your computer were still vulnerable. The specific page that you link to in your second link is presumably testing for Spectre, not Meltdown, not any of the other speculative execution security problems that have been discovered in the intervening years (after Meltdown and Spectre and before the issue being discussed in your first link), and not the issue being discussed in your first link.
2. Two previously unknown, and officially undocumented, Intel x86 instructions that, under the right circumstances, are very dangerous. This is as discussed in your first link.
Maybe a better discussion than your original link is here: https://linustechtips.com/topic/1316944-two-undocumented-x86-instructions-allegedly-found-that-can-modify-microcode/
I suspect that this research is a continuation of that linked here: Intel sec-issue (which is your topic too, so probably you already read that but maybe others have not).
If my understanding is correct, the second security problem should not be an issue for most users, unless it is blended with another exploit (or the hacker has physical access to your computer). So this problem certainly doesn’t help the overall state of computer security in the world but in isolation it may not make much difference.
Whether I am correct or not, I doubt that mitigation is available already, given that it was only announced 4 or 5 days ago. In fact, I wonder whether mitigation is even possible. @Kyle_Rankin
And I should care about Windows because?
Seriously, I would worry that you are using an old, out-of-date, unpatched browser? That in itself is a problem for you, never mind about annoying Intel CPU security problems. Please confirm what browser and version. However I won’t be able to comment as to whether you are using an appropriate browser and version on Windows.