process.c (ruby_fork_ruby): fix race in signal handling

We must block signals before stopping timer-thread, otherwise
signal handing may be delayed until (and if) another signal
is received after timer-thread is restarted.

[ruby-core:87622] [Bug #14868] [Bug #13916]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63741 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

process.c

@@ -3690,8 +3690,8 @@ rb_fork_ruby(int *status)
 
     while (1) {
 	prefork();
-	before_fork_ruby();
 	disable_child_handler_before_fork(&old);
+	before_fork_ruby();
 	pid = fork();
 	err = errno;
 	after_fork_ruby();