Pull in updated AFL instrumentation changes from AFL++

[anon8675309]

Currently Killerbeez and AFL fail with certain versions of LLVM (both too old and too new). In addition, the number of paths which are detected even in cases where it does compile without crashing (e.g. Debian 9).

AFL++ (https://github.com/vanhauser-thc/AFLplusplus) supports "llvm versions 3.8.0 to 9." which should fix some/most/all of the aforementioned problems.