cparser aborts when using __builtin_offsetof on a VLA type

[GabrielRavier]

int f(int n, int i)
{
    typedef int T[n];
    struct S
    {
        int a;
        T b[n];
    };
    return __builtin_offsetof(struct S, b[i]);
}

This results in this :

src/ast/constfold.c:756: panic in fold_expression: invalid expression kind for constant folding
Aborted (core dumped)