Don't use the global check_interrupts variable. Add a per-cpu

Don't use the global check_interrupts variable.  Add a per-cpu
checkInterrupts variable and use that to determine whether an interrupt
can occur on a given cycle.

arch/alpha/ev5.cc:
    XC -> CPU (and xc -> CPU) since we're really talking about a CPU here
    Don't use the global check_interrupts variable.  Add a per-cpu
    checkInterrupts variable and use that to determine whether an interrupt
    can occur on a given cycle.

--HG--
extra : convert_revision : be4c0247e5834005c60a45796a222cffd327b64e