Enable validateVariables(), fix fuzzing crash

[chrchr-github]

[firewave]

We need to adjust the fuzzer tests so they show the actual failure data (actually that applies to all Python tests - I want to clean that up in the future).

I think if the exitcode is negative we should show stderr instead of stdout (crashes, assert, abort, sanitizers, etc. generate negative exitcodes and our internal errors generate positive ones).

[chrchr-github]

So validateVariables() did not prevent the crash because we parse m t(=a[]); as a function declaration, and argument variables may not have a scope. What we need to verify is "Variables have a scope, or appear only in a function declaration".

[chrchr-github]

What we need to verify is "Variables have a scope, or appear only in a function declaration".

This is not so easy because of declarations like auto f(T& x) -> decltype(x);.