Allocate LDT Descriptors

Allocates one or more descriptors in the task's Local
Descriptor Table (LDT).  The descriptor(s) allocated must be
initialized by the application with other function calls.

Call With:

   AX     = 0000H
   CX     = number of descriptors to allocate

Returns:

   if function successful
   Carry flag= clear
   AX     = base selector

   if function unsuccessful
   Carry flag= set
   AX     = error code
           8011H   descriptor unavailable

Notes:

o  If more than one descriptor was requested, the function
   returns a base selector referencing the first of a
   contiguous array of descriptors.  The selector values for
   subsequent descriptors in the array can be calculated by
   adding the value returned by Int 31H Fn 0003H.
o  The allocated descriptor(s) will be set to "data" with
   the present bit set and a base and limit of zero. The
   privilege level of the descriptor(s) will match the
   application's code segment privilege level.

o   Refer to the rules for descriptor usage in Appendix D.