Always turn codegen debug assertions off in Miri

Author: saethlin

compiler/rustc_const_eval/src/interpret/step.rs

@@ -259,12 +259,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         Scalar::from_target_usize(val, self)
                     }
                     mir::NullOp::DebugAssertions => {
-                        // This should never actually lead us to any checks, because for the most
-                        // part those checks cannot be done in const-eval, and where they can be
-                        // done CTFE/Miri have better diagnostics.
-                        // But we implement the NullOp here to be correct I guess?
-                        let val = self.tcx.sess.opts.debug_assertions;
-                        Scalar::from_bool(val)
+                        // The checks hidden behind this are always better done by the interpreter
+                        // itself, because it knows the runtime state better.
+                        Scalar::from_bool(false)
                     }
                 };
                 self.write_scalar(val, &dest)?;