trans::build: Change @mut Block to &Block or &mut Block

Use &mut Block and &Block references where possible in the builder
functions in trans::build.

@mut Block remains in a few functions where I could not (not yet at
least) track down the runtime borrowck failures.

Author: blake2-ppc

src/librustc/middle/trans/base.rs

@@ -1407,7 +1407,10 @@ pub fn cleanup_and_leave(bcx: @mut Block,
     }
     match leave {
       Some(target) => Br(bcx, target),
-      None => { Resume(bcx, Load(bcx, bcx.fcx.personality.unwrap())); }
+      None => {
+          let ll_load = Load(bcx, bcx.fcx.personality.unwrap());
+          Resume(bcx, ll_load);
+      }
     }
 }