Personally, although I do use wasi-sdk (clang) and the wasm32-unknown-wasi triple, the result can be basically free-standing, depending on what flags you use.
As a sibling post said, optimization matters, and using wasm-ctor-eval and wasm-opt also helps. But it's useful to keep full C semantics.
This is what I've been doing for my little non-WASI runtime. For my minimal programs I find only a few wasi exports are required, which don't appear to actually be used and I just stub them out. Would love to figure out how to get rid of the code depending on them entirely but it's lower priority.
Also, you probably want to build a reactor (-mexec-model=reactor) if that's not what you're already doing. A command will use WASI to read command-line arguments and environment.
But it's hard to tell without knowing the specific imports you're trying to get rid of.
[0] https://github.com/s-macke/FSHistory/tree/master/src/wasm_li...