Auto merge of #146659 - cjgillot:impossible-taint, r=oli-obk

Consider errors in MIR as impossible predicates to empty the body.

The ICEs come from elaborating drops or performing state transform in MIR bodies that fail typeck or borrowck.

If the body is tainted, replace it with `unreachable`.

Fixes rust-lang/rust#122630
Fixes rust-lang/rust#122904
Fixes rust-lang/rust#125185
Fixes rust-lang/rust#139556

Author: bors