1. available_stack_size() was getting the direction wrong,
   so alloca() was never used
2. (char*) casts added to kill "break strict-aliasing rules" warnings
3. s/node/node=0/ to kill "pointer casted to integer" warning
4. added volatiles as appropriate to prevent gcc from moving
   assignment out of the loop


mysys/lf_alloc-pin.c:
  bugs/warnings fixed:
  1. available_stack_size() was getting the direction wrong,
     so alloca() was never used
  2. (char*) casts added to kill "break strict-aliasing rules" warnings
  3. s/node/node=0/ to kill "pointer casted to integer" warning
  4. added volatiles as appropriate to prevent gcc from moving
     assignment out of the loop