618409901a
`build_session` is passed an `EarlyErrorHandler` and then constructs a `Handler`. But the `EarlyErrorHandler` is still used for some time after that. This commit changes `build_session` so it consumes the passed `EarlyErrorHandler`, and also drops it as soon as the `Handler` is built. As a result, `parse_cfg` and `parse_check_cfg` now take a `Handler` instead of an `EarlyErrorHandler`.