[libFuzzer] use the new chainable malloc hooks instead of the old un-chainable ones...

[libFuzzer] use the new chainable malloc hooks instead of the old un-chainable ones, use atomic for malloc/free counters instead of a thread local counter in the main thread. This should make on-the-spot leak detection in libFuzzer more reliable

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272948 91177308-0d34-0410-b5e6-96231b3b80d8