Add #[rustc_no_mir] to make tests pass with -Z orbit.

src/test/codegen/drop.rs

@@ -11,6 +11,7 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
+#![feature(rustc_attrs)]
 
 struct SomeUniqueName;
 
@@ -24,6 +25,7 @@ pub fn possibly_unwinding() {
 
 // CHECK-LABEL: @droppy
 #[no_mangle]
+#[rustc_no_mir] // FIXME #27840 MIR has different codegen.
 pub fn droppy() {
 // Check that there are exactly 6 drop calls. The cleanups for the unwinding should be reused, so
 // that's one new drop call per call to possibly_unwinding(), and finally 3 drop calls for the