wasm: build: export bytecode modules with `-emit-llvm`
The -emit-llvm
option is needed to export bytecode together with a
.bc
extension on the output file since emscripten 3.1.50[^1].
[^1] https://github.com/emscripten-core/emscripten/commit/94b36c04dd323af066f2c1ab6d13f26eb818eb0b