Run rustfmt on tests/codegen/.

Except for `simd-intrinsic/`, which has a lot of files containing
multiple types like `u8x64` which really are better when hand-formatted.

There is a surprising amount of two-space indenting in this directory.

Non-trivial changes:
- `rustfmt::skip` needed in `debug-column.rs` to preserve meaning of the
  test.
- `rustfmt::skip` used in a few places where hand-formatting read more
  nicely: `enum/enum-match.rs`
- Line number adjustments needed for the expected output of
  `debug-column.rs` and `coroutine-debug.rs`.

tests/codegen/link-dead-code.rs

@@ -8,15 +8,21 @@
 // CHECK-LABEL: ; link_dead_code::const_fn
 // CHECK-NEXT: ; Function Attrs:
 // CHECK-NEXT: define hidden
-const fn const_fn() -> i32 { 1 }
+const fn const_fn() -> i32 {
+    1
+}
 
 // CHECK-LABEL: ; link_dead_code::inline_fn
 // CHECK-NEXT: ; Function Attrs:
 // CHECK-NEXT: define hidden
 #[inline]
-fn inline_fn() -> i32 { 2 }
+fn inline_fn() -> i32 {
+    2
+}
 
 // CHECK-LABEL: ; link_dead_code::private_fn
 // CHECK-NEXT: ; Function Attrs:
 // CHECK-NEXT: define hidden
-fn private_fn() -> i32 { 3 }
+fn private_fn() -> i32 {
+    3
+}