INT 31 P - DPMI 0.9+ - GET AND ENABLE VIRTUAL INTERRUPT STATE
        AX = 0901h
Return: CF clear
        virtual interrupts enabled
        AL = 00h if previously disabled
           = 01h if previously enabled
        AH preserved
Notes:  the previous state may be restored simply by executing another INT 31
        a STI instruction may be used if the previous state is unimportant,
          but should be assumed to be very slow due to trapping by the host
SeeAlso: AX=0902h