Don't add segfault handler in interpreter mode

...and use enum constants instead of plain numbers for referring to CPU backends.
Yes, I agree.

We currently save this field as `u8` in `Movie` and send it as `int` during netplay. Since this field probably won't have more than 256 different values any time soon and it's more important to stay compatible with , I'd say we change it to u8 and increase the netplay protocol version?