Some types in `core` are conditionally compiled based on
`target_has_atomic` or `target_has_atomic_load_store` without an
argument, for example `AtomicU64`.
This is less noticeable in Cargo projects, where rust-analyzer adds
the output `RUSTC_BOOTSTRAP=1 cargo rustc --print cfg` so it gets the
full set of cfg flags.
This fixes go-to-definition on `std::sync::atomic::AtomicU64` in
non-cargo projects.
3e51d145c3