Get CPU Mode

Returns information about the current CPU mode.  Programs
which only execute in protected mode do not need to call
this function.

Call With:

   AX     = 1686H

Returns:

   if executing in protected mode
   AX     = 0

   if executing in real mode or Virtual 86 mode
   AX     = nonzero

Notes:

o  Some environments support programs or libraries that can
   execute in either real or protected mode (bimodal code).
   This function is supplied so that such programs can
   detect at run time whether they are running in protected
   mode and make use of system facilities accordingly.
o  This function should not be used to determine if a DPMI
   host is present.  A client should make sure that DPMI
   services are available before calling this function;
   otherwise, the results returned by the function may not
   be valid.