- Turn off KVM_WERROR by default for all configs so that it's not
inadvertantly enabled by non-KVM developers, which can be problematic for
subsystems that require no regressions for W=1 builds.
- Advertise all of the host-supported CPUID bits that enumerate IA32_SPEC_CTRL
"features".
- Don't force a masterclock update when a vCPU synchronizes to the current TSC
generation, as updating the masterclock can cause kvmclock's time to "jump"
unexpectedly, e.g. when userspace hotplugs a pre-created vCPU.
- Use RIP-relative address to read kvm_rebooting in the VM-Enter fault paths,
partly as a super minor optimization, but mostly to make KVM play nice with
position independent executable builds.