Building for WebGL didn't work on my system either. I am contemplating to install Unity on that small-ish laptop I got recently and temporarily activate the second license to try to build on a Windows system. (Would anyone think that a machine with a Celeron N4020, 4GB memory and a 1366x768 screen makes for a good game development machine? Right, I don't, either... But for just opening the editor to load the project and perform one single build taks, it should be able to survive...)
I ended up installing it on my work laptop - hours of downloading later - pulled down my repo, and the same problem! An odd emscripten error that seemingly only two people on the internet had ever had before. Fun times until 2am, but hey that's developer life!!
Fortunately I'd taken today off work and was able to resolve it this morning by creating a fresh project and porting across the changes.
Hope you enjoyed the gamejam and you got it working in the end.