Bugfix: Allow building libbitcoinconsensus without any univalue

[luke-jr]

No description provided.

[theuni]

Concept ACK. A few nits:

• Please store the test as build_no_programs or build_libs_only or so, so that we only need the ugly xnononono stuff in one place.
• I'd rather not abuse system_univalue that way, as it's not obvious what it's doing. Please change that to configure_embedded_univalue or so, and rework the test as necessary.

[luke-jr]

It's conceivable that at some point bitcoin-tx could be freed of the univalue dependency as well, so I'm not sure it makes sense to do the dedicated var?

[laanwj]

I don't think that's realistic. bitcoin-tx uses JSON objects in various places in the interface

[theuni]

@luke-jr My only concern is that "system_univalue" should not be equated to "don't use any univalue". renaming to need_univalue would suffice.

[laanwj]

Ok, let's rename it then.

[luke-jr]

Renamed.

[theuni]

Thanks. utACK.

[jgarzik]

ut ACK

[luke-jr]

Needs backport to 0.13.