stack redzone

[Maxime Villard <max%m00nbsd.net@localhost>]

Here is a patch [1] that adds a redzone between the pcb and the kernel stack.
The point is that if the kernel goes into an infinite/toodeep call recursion,
we don't want it to overflow the pcb and the potentially sensitive kernel
data sitting below the pcb.

With this patch, we get a #DF exception which causes a clean panic.

Maxime

[1] https://m00nbsd.net/garbage/x86/stack-redz.diff