CLEANUP: tree-wide: fix prototypes for functions taking no arguments.

CLEANUP: tree-wide: fix prototypes for functions taking no arguments.

"f(void)" is the correct and preferred form for a function taking no
argument, while some places use the older "f()". These were reported
by clang's -Wmissing-prototypes, for example:

  src/cpuset.c:111:5: warning: no previous prototype for function 'ha_cpuset_size' [-Wmissing-prototypes]
  int ha_cpuset_size()
  include/haproxy/cpuset.h:42:5: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
  int ha_cpuset_size();
      ^
                     void

This aggregate patch fixes this for the following functions:

   ha_backtrace_to_stderr(), ha_cpuset_size(), ha_panic(), ha_random64(),
   ha_thread_dump_all_to_trash(), get_exec_path(), check_config_validity(),
   mworker_child_nb(), mworker_cli_proxy_(create|stop)(),
   mworker_cleantasks(), mworker_cleanlisteners(), mworker_ext_launch_all(),
   mworker_reload(), mworker_(env|proc_list)_to_(proc_list|env)(),
   mworker_(un|)block_signals(), proxy_adjust_all_maxconn(),
   proxy_destroy_all_defaults(), get_tainted(),
   pool_total_(allocated|used)(), thread_isolate(_full|)(),
   thread(_sync|)_release(), thread_harmless_till_end(),
   thread_cpu_mask_forced(), dequeue_all_listeners(), next_timer_expiry(),
   wake_expired_tasks(), process_runnable_tasks(), init_acl(),
   init_buffer(), (de|)init_log_buffers(), (de|)init_pollers(),
   fork_poller(), pool_destroy_all(), pool_evict_from_local_caches(),
   pool_total_failures(), dump_pools_to_trash(), cfg_run_diagnostics(),
   tv_init_(process|thread)_date(), __signal_process_queue(),
   deinit_signals(), haproxy_unblock_signals()