INT 31H 0901H: Query and Disable Virtual Interrupt State

                                                    Compatibility: DPMI 0.9+ 
 Expects: AX    0901H
 Returns: CF    NC (clear; always successful)
          AL    previous setting: 00H = virtual interrupts were disabled
                                  01H = virtual interrupts were enabled
    Info: Enables the virtual interrupt flag and returns the previous state
          of that flag.

          AH is not modified by the call, so you can return to the previous
          state immediately by calling INT 31H.

          If you don't need to know the previous state, you may simply use
          the STI opcode.

See Also: DPMI API
          INT 2fH: Multiplex Interrupt
          DOS Functions