We might be passing through CPUID bits that we should not be to the guest, at
least not without adding that MSR to our emulation list.
I'm not sure how we handle spectre/meltdown representations to guests on Intel.
I don't think guests should be able to set these MSRs and they probably
shouldn't do software mitigation -- it's up to the host to correct mitigate.
So maybe we should set whatever bit claims immunity to spectre/meltdown in