Mark some compiler structs as public

[xtuc]

Refs https://github.com/stalwartlabs/sieve/issues/3

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}