Protobuf Now Mandatory about monero

[selsta]

Trezor is still optional so the CMake has to be fixed, will take a look at it.

[vtnerd]

I think its just that it defaults to on (looking at a fix myself).

[vtnerd]

@selsta got owned by the CMakeCache again.

This variable defaults to compile Trezor in, which then triggers a requirement for Protobuf. Whereas previously, no explicit opt-out was required.

It seems like this could be flipped to default off, requiring users to opt-in, but we may need to tag the Trezor/Protobuf team on this.

[selsta]

I think the behaviour should be changed so that if protobuf isn't installed it should print a warning that Trezor compilation is skipped, not fail. Only if USE_DEVICE_TREZOR_MANDATORY is enabled it should fail.

Keeping USE_DEVICE_TREZOR on by default should be fine as long as it doesn't cause the compilation to fail.