bpf-fuzzer | fuzzing framework based on libfuzzer and clang sanitizer

The "setup" target creates common symbolic links and download and build llvm fuzzer. It only needs to run once. The "all" target builds two binaries, test_verifier and test_fuzzer. test_verifier is essentially linux/samples/bpf/test_verifier.c with slight modification to adapt to the new test framework, with sanitizer support. test_fuzzer uses llvm fuzzer framework for testing. test_verifier can also generate initial test cases for test_fuzzer. These test cases will make fuzzer more effective in generating relevent new test cases. To report memory leaks, the test_fuzzer needs to terminate normally. This can be done by limiting the number of runs, e.g.,.