Replace printf PRIxMAX specifier with '%p' for thread id debug output

Replace printf PRIxMAX specifier with '%p' for thread id debug output

* pthread_support.c (GC_new_thread, GC_delete_thread,
GC_delete_gc_thread, GC_unregister_my_thread_inner,
GC_unregister_my_thread, GC_thread_exit_proc,
GC_start_rtn_prepare_thread, pthread_create): Output thread id value
(when DEBUG_THREADS) using %p format specifier instead of PRIxMAX, %x
and %lx (casting passed id value to pointer type instead of uintmax_t).
* pthread_start.c (GC_inner_start_routine): Likewise.
GC_stop_world, GC_thread_resume, GC_start_world): Likewise.
* pthread_stop_world.c (GC_suspend_handler_inner, GC_restart_handler,
GC_push_all_stacks, GC_suspend_all, GC_stop_world, GC_start_world):
Likewise.
* darwin_stop_world.c (GC_stack_range_for, GC_suspend_thread_list,
* pthread_start.c: Do not include inttypes.h.
* pthread_support.c: Likewise.
* pthread_support.c (GC_count_threads): Define only if DEBUG_THREADS.
* pthread_support.c (GC_unregister_my_thread): Rename gc_self local
variable to "me".
* pthread_support.c (pthread_create): Report thread started (when
DEBUG_THREADS) only if result is 0.