The whole stack is C++ game code that uses C raylib compiled for Emscripten via CMake. With gcc it was just fine and I frankly quite liked raylib there. It has a very minimalistic interface that is to my liking. Building it with gcc or msvc via CMake was rather straight-forward (altough they don't distribute cmake files with their releases, so you need to clone repo and build/install yourself).
Two major problems were with Emscripten: first being system headers redefining max_align_t because of unmatching guards between them and libcxx headers - I resolved it by hotfixing system headers, the other problem was guards in math.h conflicting with cmath that caused missing definitions and symbols - I resolved that by downgrading includes to math.c, because all I needed was sin/cos functions.