unsafe fn write_clone_into_raw(&self, target: *mut Self) {
        // We can always copy in-place, without ever involving a local value.
        unsafe { target.copy_from_nonoverlapping(self, 1) };
    }
HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
they cannot call `Self::new()`.

If you change `RawVec<T>::new` or dependencies, please take care to no
benchmarks/haystacks/code/rust-library.rs