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/instrument-coverage/instrument-coverage.rs

@@ -12,12 +12,10 @@
 // CHECK: @__llvm_profile_filename = {{.*}}"default_%m_%p.profraw\00"{{.*}}
 // CHECK: @__llvm_coverage_mapping
 
-#![crate_type="lib"]
+#![crate_type = "lib"]
 
 #[inline(never)]
-fn some_function() {
-
-}
+fn some_function() {}
 
 pub fn some_other_function() {
     some_function();