Forkserver example with forkserver.c

[tokatoka]

Andrea has ported forkserver logic from afl++ https://github.com/AFLplusplus/LibAFL/blob/main/libafl_targets/src/forkserver.c

Our current forkserver example forksever_simple uses afl++'s compiler to instrument the program, but we want to make a forkserver example that uses libafl_cc + our forkserver logic in libafl_targets