Pull up following revision(s) (requested by christos in ticket #653):
sys/arch/i386/include/profile.h: revision 1.36
sys/arch/i386/include/profile.h: revision 1.37

- prevent optimization from omitting the frame pointer (and re-using it);
  we use it in our inline assembly.
- convert to c a little assembly to make the code more understandable.

use compiler builtins to compute addresses instead %ebp assembly arithmetic.
(from joerg)

(martin)