fix#115348fix#115348
It looks that:
- In `rustc_mir_build::build`, the body of function will not be built, when the `tcx.check_match(def)` fails due to `non-exhaustive patterns`
- In `rustc_mir_transform::check_unsafety`, the `UnsafetyChecker` collects all `used_unsafe_blocks` in the MIR of a function, and the `UnusedUnsafeVisitor` will visit all `UnsafeBlock`s in the HIR and collect `unused_unsafes`, which are not contained in `used_unsafe_blocks`, and report `unnecessary_unsafe`s
- So the unsafe block in the issue example code will be reported as `unnecessary_unsafe`.
3e42a12a54