Auto merge of #43748 - RalfJung:mir-validate2, r=arielb1

AddValidation: handle Call terminators into blocks that have multiple incoming edges

The old code was just wrong: It would add validation on paths that don't even come from the call, and it would add multiple validations if multiple calls end return to the same block.

diff --cc src/librustc_driver/driver.rs
Simple merge