Auto merge of #156274 - lokirithm:reorg-tests-03, r=wesleywiser

Reorg tests 03

| old-name | new-sub-dir | new-name |
|-|-|-|
| `issue-38727.rs` [issue](https://github.com/rust-lang/rust/issues/38727) | `abi/` | `return-ref-as-immediate-in-codegen.rs` |
| `issue-38437.rs` [issue](https://github.com/rust-lang/rust/issues/38437) | `mir/` | `reset-discriminant-drop-flag-on-partial-move.rs` |
| `issue-31910.rs` [issue](https://github.com/rust-lang/rust/issues/31910) | `associated-consts/` | `associated-const-in-enum-discriminant.rs` |
| `issue-31910.stderr` | `associated-consts/` | `associated-const-in-enum-discriminant.stderr` |
| `issue-48159.rs` [issue](https://github.com/rust-lang/rust/issues/48159) | `packed/` | `packed-c-style-struct.rs` |

r? Kivooeo

tests/ui/abi/return-ref-as-immediate-in-codegen.rs

@@ -1,3 +1,4 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/38727>
 //@ build-pass
 #![allow(dead_code)]
 #[repr(u64)]

tests/ui/associated-consts/associated-const-in-enum-discriminant.rs

@@ -1,3 +1,4 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/31910>
 enum Enum<T: Trait> {
     //~^ ERROR: `T` is never used
     //~| NOTE: unused type parameter

tests/ui/associated-consts/associated-const-in-enum-discriminant.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/issue-31910.rs:4:9
+  --> $DIR/associated-const-in-enum-discriminant.rs:5:9
    |
 LL |     X = Trait::Number,
    |         ^^^^^^^^^^^^^ expected `isize`, found `i32`
@@ -7,7 +7,7 @@ LL |     X = Trait::Number,
    = note: enum variant discriminant can only be of a primitive type compatible with the enum's `repr`
 
 error[E0392]: type parameter `T` is never used
-  --> $DIR/issue-31910.rs:1:11
+  --> $DIR/associated-const-in-enum-discriminant.rs:2:11
    |
 LL | enum Enum<T: Trait> {
    |           ^ unused type parameter

tests/ui/mir/reset-discriminant-drop-flag-on-partial-move.rs

@@ -1,3 +1,4 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/38437>
 //@ run-pass
 #![allow(dead_code)]
 // Check that drop elaboration clears the "master" discriminant

tests/ui/packed/packed-c-style-struct.rs

@@ -1,3 +1,4 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/48159>
 //@ run-pass
 #![allow(non_camel_case_types)]