In combination with Doug's recent alpha_cpu.h, this reduces the cost
of ipl raising/lowering significantly. This is most pronounced when
doing file reads.
Reviewed by: dfr
work in progress and has never booted a real machine. Initial
development and testing was done using SimOS (see
http://simos.stanford.edu for details). On the SimOS simulator, this
port successfully reaches single-user mode and has been tested with
loads as high as one copy of /bin/ls :-).
Obtained from: partly from NetBSD/alpha
