Set CR4[18] OSXSAVE in cr4_guest_host_mask

[clydergriffin]

Set CR4[18] OSXSAVE in cr4_guest_host_mask

During boot Windows 11 as a guest VM was
faulting on XSETBV instruction because
CR4[18] OSXSAVE was not set. (XSETBEV is
undefined if CR4[18] OSXSAVE is not set.)

This patch sets cr4_guest_host_mask[18]
causing the the corresponding cr4 shadow
register to virtualize the state of
CR4[18].  This results in a more robust
CR4 implementation and removes the chance
of CR4[18] OSXSAVE corruption.