add stubs to allow compilation under GOOS=tamago

[abarisani]

The TamaGo bare metal framework would benefit from being able to integrate go-git on bare metal firmware.

This PR, in combination with this go-git PR adds the required stubs to allow compilation under GOOS=tamago.

Thanks

[pjbgf]

It would be great to have tests to ensure we won't get regressions in the future. Can you please add something around the lines of what we have for wasi or wasm?

[abarisani]

It would be great to have tests to ensure we won't get regressions in the future. Can you please add something around the lines of what we have for wasi or wasm?

This would require downloading and using our own compiler rather than stock Go, would you be fine with this? (for all intents and purposes we are identical to js at this point)

[pjbgf]

@abarisani yep, that's fine. Something around the likes of #44 should be OK.