This error may occur is the local clang installation does not have a version of
libclang_rt built for WebAssembly, for example:
wasm-ld: error: cannot open {...}/lib/wasi/libclang_rt.builtins-wasm32.a: No such file or directory
clang-9: error: linker command failed with exit code 1 (use -v to see invocation)
This article describes how to solve the issue https://depth-first.com/articles/2019/10/16/compiling-c-to-webassembly-and-running-it-without-emscripten/ which instructs to download precompiled versions of the library distributed at https://github.com/jedisct1/libclang_rt.builtins-wasm32.a and install them at the location where clang expects to find them (the path in the error message).
Here is a direct link to download the library.