Adds a comment that reports a relatively recent security vulnerability that forces eager
saving and restoration of FPU state for every task/context switch. These changes might
make the execution of an xmm-related inst in signal_arch_init unnecessary.
Yet, it does not remove this inst execution, given that older kernels will not have this fix
and since eager FPU state save/restore mitigates transparency concerns (this instruction
execution essentially will have minimum (if any) visible effect on recent kernels).