Reported by Coverity:

    ID 1406102:  Incorrect expression  (ASSERT_SIDE_EFFECT)
    /bin/varnishtest/vtc_http2.c: 852 in receive_frame()
    846                         s->wf = 0;
    847                         AZ(pthread_cond_signal(&s->cond));
    848                 }
    849                 continue;
    850         }
    851         AZ(pthread_mutex_unlock(&hp->mtx));
    >>> CID 1406102:  Incorrect expression  (ASSERT_SIDE_EFFECT)
    >>> Argument "vtc_error" of assert() has a side effect because the
    >>> variable is volatile.  The containing function might work
    >>> differently in a non-debug build.
    852         assert(vtc_error || vsb == NULL);
    853         return (NULL);
    854 }
    855
    856 #define STRTOU32(n, ss, p, v, c)                             \
    857         do {                                                 \

Although I'm not sure how relevant it is since assert() from vas.h
doesn't remove side effects when no-op'd.