signal.c: get rid of heap corruption
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47984 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
signal.c: get rid of heap corruption
of heap corruption by alternate stack overflow in SEGV handler.
typically happened at fprintf() in control_frame_dump().
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47984 b2dd03c8-39d4-4d8f-98ff-823fe69b080e