I removed some lint configuration in the process:
* `#[allow(clippy::suspicious_else_formatting)]` because nothing is
currently triggering it.
* `#[warn(clippy::future_not_send)]` because some stuff under
`src/lib.rs` is. And also like, auto-trait leakage generally means
this isn't a problem, and if things really need to be `Send`, then
you'll probably know to mark it manually.
* `#[warn(rust_2018_idioms)]` and replaced it with
`explicit-outlives-requirements = "warn"` which is the most useful
lint in that group that isn't enabled by default.
It comes with a bunch of new lints (yay!) so I fixed them all so CI will
keep working.
Also apparently something about linking changed because I had to change
the checks for deciding the linker flags for static x86_64 builds to
keep working.
