v8 is pretty complicated, and anything that depends on LLVM is going to be huge, so I think I would start smaller. You could try building around something like NuttX or an L4 + tcc or cproc and see what it takes to get to self-hosting as well as ability to do some job you care about. To me the bigger question is that last bit, you can shrink the platform code quite a lot relative to a typical Linux but what's the situation where that's a good trade vs say cross-compiling from a full C++ or Rust toolchain?