vm_trace.c: suppress warning
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38384 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
vm_trace.c: suppress warning
RB_UNUSED_VAR().
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38384 b2dd03c8-39d4-4d8f-98ff-823fe69b080e