The Nim binary dynamically links against glibc and SDL2. If you really want to statically link against a C standard library, musl works just fine:

    @if musl:
      passL = "-static"
      gcc.exe = "/usr/local/musl/bin/musl-gcc"
      gcc.linkerexe = "/usr/local/musl/bin/musl-gcc"
    @end

Now it compiles like this (SDL2 is still dynamically loaded, +1 MB for that):

    $ nim -d:release -d:musl c src/nimes
    $ ls -lha src/nimes
    -rwxr-xr-x 1 def users 219K Mai  1 22:00 src/nimes*

If the Nim binary is dynamically linked, comparing the size to a Go binary isn't always valid. There are reasonable trade-offs to consider when selecting dynamic vs static linking. Admittedly, when you're running an NES emulator on your desktop probably isn't one of them, you're not likely to care either way.

The Nim -> C -> emscripten path is very impressive. Kudos.