Avoid `SmallVec::collect()` in `Result::intern_with()`.
Avoid `SmallVec::collect()` in `Result::intern_with()`.

This commit reduces instruction counts for several benchmarks by up to
5%.

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