clone bug in rustc_index::bit_set::BitSet

[LeeeWee]

In the following code from rust/compiler/rustc_index/src/bit_set.rs, self.words should resize with from.words.len() instead of from.domain_size.

    fn clone_from(&mut self, from: &Self) {
        if self.domain_size != from.domain_size {
            self.words.resize(from.domain_size, 0);
            self.domain_size = from.domain_size;
        }

        self.words.copy_from_slice(&from.words);
    }

Otherwise, this function will panic when calling 'copy_from_slice' because of the mismatched slice length.