clang-tidy fails with version 15+

[ckreibich]

I noticed this during a routine CI config update (#364). Details on Cirrus. The update currently sidesteps this by sticking with a distro that still uses llvm 14, but sooner or later this will need resolving. The exact set of errors depends on the clang-tidy version, but the good news is that it's just a handful. In the above run:

/broker/caf/libcaf_core/caf/config_value.hpp:550:7: error: Undefined or garbage value returned to caller [clang-analyzer-core.uninitialized.UndefReturn,-warnings-as-errors]
      return std::move(*val);
      ^

/broker/caf/libcaf_core/caf/config_value.hpp:106:5: error: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage,-warnings-as-errors]
    set(std::forward<T>(x));
    ^

As these straddle Broker and CAF I'm not sure how to proceed — seems Broker's clang-tidy run should not complain about things it finds in CAF, since CAF has its own clang-tidy setup. I can't tell if Broker is doing anything wrong in its use of those CAF APIs.

One idea I had was to treat the CAF headers as system headers, so there's a way to mute their findings, but I couldn't get that to work.

[Neverlord]

Weird, we set HeaderFilterRegex: 'broker/.*.hh' in the clang-tidy file to ignore everything from other sources. Let me look into it.

[Neverlord]

I can see that diagnostic locally with 16.0.5 as well. I have no idea why it thinks that could be a garbage value. That line just unpacks an expected value. Looks like a false positive to me. I'll maybe try tweaking it a bit and otherwise add a NOLINT there.