missing/setproctitle.c: Avoid invalidating argv[1], argv[2], etc. until the first call to Process.setproctitle, because the ps command of AIX refers to the argv array. [Bug #10090]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47852 b2dd03c8-39d4-4d8f-98ff-823fe69b080e