https://github.com/parcel-bundler/parcel
For comparison purposes:
https://github.com/skx/implant
My code is smaller, but it doesn't contain the filesystem-walker, etc.
I have some hard times to make COFF works. Have you tried to compile syso files within your go binaries for Darwin?
https://github.com/gobuffalo/packr
https://github.com/parcel-bundler/parcel