clang and ECL both seem interesting, as long as LGPL license is ok. They both are complex to embed though - neither are well tuned to be embedded in other applications. (I've been exploring on MacOS). Julia could be interesting too under same questions (and a better license for commercial products) but similarly has a fair bit of glue code needed - especially if you want to restrict (say) filesystem access.

Oh right, that was a thing too. LGPL would have complicated some plans. Forgot that details.