Use -Z force-dropflag-checks=on/off for emitting sanity-check.

Author: pnkfelix

src/librustc_trans/trans/glue.rs

@@ -237,7 +237,7 @@ fn trans_struct_drop_flag<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
     let drop_flag_llty = type_of(bcx.fcx.ccx, bcx.tcx().dtor_type());
     let init_val = C_integral(drop_flag_llty, adt::DTOR_NEEDED as u64, false);
 
-    let bcx = if bcx.tcx().sess.opts.debuginfo == NoDebugInfo {
+    let bcx = if !bcx.ccx().check_drop_flag_for_sanity() {
         bcx
     } else {
         let drop_flag_llty = type_of(bcx.fcx.ccx, bcx.tcx().dtor_type());