thread_sync.c (condvar_ptr): reset fork_gen after forking

Otherwise the condition variable waiter list will always
be empty, which is wrong :x

[Bug #14725] [Bug #14634]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63309 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread_sync.c

@@ -1308,6 +1308,7 @@ condvar_ptr(VALUE self)
 
     /* forked children can't reach into parent thread stacks */
     if (cv->fork_gen != fork_gen) {
+        cv->fork_gen = fork_gen;
         list_head_init(&cv->waitq);
     }