(Ada/AArch64) fix fixed point argument passing in inferior funcall

(Ada/AArch64) fix fixed point argument passing in inferior funcall

Consider the following code:

   type FP1_Type is delta 0.1 range -1.0 .. +1.0; --  Ordinary

   function Call_FP1 (F : FP1_Type) return FP1_Type is
   begin
      return F;
   end Call_FP1;

When the default in GCC is to generate proper DWARF info for fixed point
types, then in gdb, printing the result of a call to call_fp1 with a
decimal parameter leads to:

  (gdb) p call_fp1(0.5)
  $1 = 0

The displayed value is wrong, and we actually expected:

  (gdb) p call_fp1(0.5)
  $1 = 0.5

What happened is that our fixed point type parameter got promoted to a
32bit integer because we detected that the length of that object was less
than 4 bytes. The compiler does not perform this promotion and therefore
GDB should not either.

This patch fixes the behavior described above.