Add hack to silence the annoying liveness warning in trans/base.rs.

src/rustc/middle/trans/base.rs

@@ -3857,6 +3857,7 @@ fn trans_break_cont(bcx: block, to_end: bool)
     // Locate closest loop block, outputting cleanup as we go.
     let mut unwind = bcx;
     let mut target = bcx; // FIXME---not necc. but tstate thinks it is
+    let _target = target; // FIXME---hack to shut up liveness about target
     loop {
         alt unwind.kind {
           block_scope({loop_break: some(brk), _}) {