When cryb-test is used as a framework for another project, the compile-time test is useless since cryb-test itself will have been built with coverage disabled. Besides, it is not a reliable indicator of whether leak detection will work. Instead, check if the heap is already dirty when we first gain control.
All further instances of asprintf() or vasprintf() in our codebase are either in libcryb-test or in individual unit tests, and in all cases, the only consequence of a failed call is that the result will say "no description" instead of either a description of the test or an explanation of how it failed. Therefore, we can simply ignore the problem and cast the call to void to satisfy gcc.
