rustc: replace a few `.cloned()` with `.copied()`.
rustc: replace a few `.cloned()` with `.copied()`.

aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust