Auto merge of #161031 - jhpratt:rollup-XTZ644V, r=jhpratt

Rollup of 8 pull requests

Successful merges:

 - rust-lang/rust#159593 (merge ambiguity errors that blame the same inference variable)
 - rust-lang/rust#160687 (Experiment: Add `core::cmp::smallest` and `core::cmp::largest`)
 - rust-lang/rust#160856 (Replace infers and non-rigid aliases with `Ty/Const::Error` if param env normalization fails)
 - rust-lang/rust#160961 (bootstrap: Overhaul matching of command-line selectors to steps)
 - rust-lang/rust#160975 (Remove target argument from get_proc_macros)
 - rust-lang/rust#161023 (bootstrap: Replace the `exit!` macro with a function `helpers::exit_process`)
 - rust-lang/rust#160932 (Make tidy::Version public)
 - rust-lang/rust#161029 (mailmap: Update my default email)