vm_backtrace.c: copy without creating prefix string
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43207 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
vm_backtrace.c: copy without creating prefix string
directly, without creating prefix string.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43207 b2dd03c8-39d4-4d8f-98ff-823fe69b080e