[libFuzzer] implement a better queue for the fork mode. Add an internal flag -stop_file to allow graceful shutdown of fuzzing. Enhance the logging in the fork mode

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer@363470 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed