Ruby

vm*: doubly-linked list from ccan to manage vm->living_threads

A doubly-linked list for tracking living threads guarantees
constant-time insert/delete performance with no corner cases of a
hash table. I chose this ccan implementation of doubly-linked
lists over the BSD sys/queue.h implementation since:

1. insertion and removal are both branchless
2. locality is improved if a struct may be a member of multiple lists
   (0002 patch in Feature 9632 will introduce a secondary list
   for waiting FDs)

This also increases cache locality during iteration: improving
performance in a new IO#close benchmark with many sleeping threads
while still scanning the same number of threads.

    vm_thread_close 1.762

• vm_core.h (rb_vm_t): list_head and counter for living_threads
  (rb_thread_t): vmlt_node for living_threads linkage
  (rb_vm_living_threads_init): new function wrapper
  (rb_vm_living_threads_insert): ditto
  (rb_vm_living_threads_remove): ditto
• vm.c (rb_vm_living_threads_foreach): new function wrapper
• thread.c (terminate_i, thread_start_func_2, thread_create_core,
  thread_fd_close_i, thread_fd_close): update to use new APIs
• vm.c (vm_mark_each_thread_func, rb_vm_mark, ruby_vm_destruct,
  vm_memsize, vm_init2, Init_VM): ditto
• vm_trace.c (clear_trace_func_i, rb_clear_trace_func): ditto
• benchmark/bm_vm_thread_close.rb: added to show improvement
• ccan/build_assert/build_assert.h: added as a dependency of list.h
• ccan/check_type/check_type.h: ditto
• ccan/container_of/container_of.h: ditto
• ccan/licenses/BSD-MIT: ditto
• ccan/licenses/CC0: ditto
• ccan/str/str.h: ditto (stripped of unused macros)
• ccan/list/list.h: ditto
• common.mk: add CCAN_LIST_INCLUDES
  [ruby-core:61871][Feature 9632 (part 1)]

Apologies for the size of this commit, but I think a good
doubly-linked list will be useful for future features, too.
This may be used to add ordering to a container_of-based hash
table to preserve compatibility if required (e.g. feature 9614).

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45913 b2dd03c8-39d4-4d8f-98ff-823fe69b080e