vm_core: use "int" for living_thread_num

We treat this as "int" through the vm_living_thread_num API
anyways, and "pid_t" is still 32-bits with glibc on 64-bit
platforms.  I expect it'll be a long time before anybody needs
more than 2 billion native threads.  For now, let's save one
cacheline on x86-64 (as reported by pahole(1)):

	before:  size: 1288, cachelines: 21, members: 45
	 after:  size: 1280, cachelines: 20, members: 45

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62075 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 1 deletions

diff --git a/vm_core.h b/vm_core.h
index 176ec9d333..8bce7892b5 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -526,8 +526,8 @@ typedef struct rb_vm_struct {
 
     struct list_head waiting_fds; /* <=> struct waiting_fd */
     struct list_head living_threads;
-    size_t living_thread_num;
     VALUE thgroup_default;
+    int living_thread_num;
 
     unsigned int running: 1;
     unsigned int thread_abort_on_exception: 1;