[clang] [llvm] [analyzer] New checker: optin.core.UnconditionalVAArg (PR #175602)

[Donát Nagy via cfe-commits]

NagyDonat wrote:

It seems that my checker can produce false positives when `va_arg()` is called within a `switch` statement (which introduces separate branches without activating a `BranchCondition` callback).

I found an example of this during the analysis of the `sqlite` project, which confirms that consistently testing patches on a set of real-world projects is a good thing to do.

I'll come up with a fix for this issue within a few days.

https://github.com/llvm/llvm-project/pull/175602