2b259577aa
Add FileCheck annotations to dataflow-const-prop tests part of #116971. A few shadowing variable names are changed, so that it is easier to match the variable names in MIR using FileCheck syntax. Also, there's a FIXME in [enum.rs](https://github.com/rust-lang/rust/pull/119759/files#diff-7621f55327838e489a95ac99ae1e6126b37c57aff582594e6bee9d7e7e56fc58) because the MIR looks suspicious to me. It has been explained in the comments. r? cjgillot