This should be safe. Rarely is `'` used as syntax in a language that
separates literals.
- `'` is used within hex literals in C++ but we want to treat them as
one word
- `'` is used for lifetimes in Rust but there are other symbols on the
left side.
This was inspired by heck. They have an invariant to ensure this isn't
a problem (only accept `_` as boundary) while on the other hand we
accept a lot of things as boundaries.