add stanc version to output of bin/stanc --version

[avehtari]

Summary:

bin/stanc --version

prints

stanc version 2.22.0

It would be useful to show also whether stanc2 or stanc3 is used

Current Version:

v2.22.0

[wds15]

I am not sure this is useful. The plan is definitely to drop stanc2 entirely. There will only be a single stanc for a given cmdstan version. @mitzimorris should weigh in here, but I would not think that we need this.

[avehtari]

As long as there are two options, there should be a way to see which is actually used. It seems this will be fixed in stanc3 stan-dev/stanc3#443, see also stan-dev/cmdstanr#115

[rok-cesnovar]

In order to distinguish until we have both, stanc3 will output stanc3 on 2.22.1+. The fix was already merged so I am going to close this.

After the old compiler is phased out we can come back to this.