Correct a hang when we boot with EMILE:
Problem: in start_kernel(), kernel hangs on the sti().
Analyse: We can suppose there are pending IRQs when we
unmask them, and
unfortunately handlers are not already installed.
Penguin booter doesn't meet the issue because it makes
a shutdown under MacOS
that should clear IRQs.
Solution: To avoid this case, we must avoid pending
IRQs by disabling/clearing
IRQs when we clear handlers (in mac_init_IRQ).
Tested on the machine where the problem appears, a
Performa 450/LCIII, the
patch corrects the problem.
Tested on a machine where the problem doesn't appear, a
IIci, kernel continues
to work correctly :-P