cxx.cc in the way of wasm32-* support

I was trying to compile a rust project depending on autocxx and cxx for wasm32-* targets and faced issues because cxx's cxx.cc uses the C++ standard library, which may not yet be available when the project's dependencies are being compiled (it becomes available during the execution of the project's build.rs).

I tried playing around with cxx to see if I can safely exclude cxx.cc and/or find it behind a feature. I was surprised to discover that if I clear the file completely, cxx still successfully compiles (now for wasm32-* targets, too) and seems to work.

So, I wonder: what are the effects of excluding cxx.cc? Which parts of it cannot be excluded safely? What do you think would be the right way to enable cxx to support web assembly (ideally, the wasm32-unknown-unknown target, which cannot rely on the C++ standard library)?