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/lib-optimizations/iter-sum.rs

@@ -2,7 +2,6 @@
 //@ only-x86_64 (vectorization varies between architectures)
 #![crate_type = "lib"]
 
-
 // Ensure that slice + take + sum gets vectorized.
 // Currently this relies on the slice::Iter::try_fold implementation
 // CHECK-LABEL: @slice_take_sum