* miscfuncs.cc (tls_ix): Predefine.
* perthread.h (set_reent): Eliminate.
(get_reent): Ditto.
* winbase.h (my_tlsalloc): Use global stack base pointer. Set newly allocated
location to NULL.
(my_tlssetvalue): Use global stack base pointer.
(my_tlsgetvalue): Ditto.