thread.c: threadptr_pending_interrupt_active_p is static

It's not used elsewhere.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61749 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread.c

@@ -1743,7 +1743,7 @@ rb_threadptr_pending_interrupt_deque(rb_thread_t *th, enum handle_interrupt_timi
 #endif
 }
 
-int
+static int
 threadptr_pending_interrupt_active_p(rb_thread_t *th)
 {
     /*