DW      FLOODFILL       ; Fill a bounded region using a flood fill

  Input:
     AX         The x coordinate for the seed point
     BX         The y coordinate for the seed point
     CL         The boundary color for the Flood Fill

  Return:
     Nothing      (Errors are returned in Device Status STAT field).

This function is called to fill a bounded region on bitmap devices. The
(X,Y) input coordinate is used as the seed point for the flood fill. (CP)
becomes the seed point. The current FILLPATTERN is used to flood the
region.