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

Reorg tests 03

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

r? Kivooeo

Author: bors