chore: support building libstrophe as a subproject

[paulfertser]

When pkg-config doesn't find usable libstrophe this will download and build it automatically.

[sjaeckel]

Huge 👎 from me on this.

Only because one can do something doesn't necessarily mean it's a good idea.

Next step would then be if there's no compiler you download the GCC sources and build that one?

[paulfertser]

Yes, I'm not sure. You have automatic dependency resolution and installation for binary packages in most GNU/Linux distros.
Here I feel like it might be nicer for development when everything is self-contained, kind of like maintenance-free git submodules, and you can go and build right away with whatever changes in one copy and with different changes in another copy and not worry about setting PKG_CONFIG_PATH manually or polluting your /usr/local etc, and run directly from this build dir and remove it all in one go when done.

[jubalh]

I like the change.
Because libstrophe and Profanity are so tightly connected.

Sometimes it happens that we need a change on libstrophe. Usually then jaeckel implemented in there.
With this change it would be very easy for people to test it without the need to learn how to setup libstrophe git independently on their system.

We have had this a couple of times in the past, probably the issues are tagged depends-on-libstrophe.

So we get a new feature request/bug -> it needs a change in libstrophe -> change is implemented there but only on master -> people can use this feature to build profanity with latest git libstrophe -> people can easily test and give feedback/use the new feature.

What I'm unsure about is the When pkg-config doesn't find usable libstrophe part.
Like this it really can be confusing that people might just have forgotten to install libstrophe on their system via the package manager and by accident use libstrophe git.
Also developers who have libstrophe installed can't decide "I want to test with libstrophe git now" without uninstalling their system libstrophe first.

So I think I would prefer to have this via a switch?
What do you guys think?