[libFuzzer] use 'if guard' instead of 'if guard >= 0' with trace-pc; change...

[libFuzzer] use 'if guard' instead of 'if guard >= 0' with trace-pc; change the guard type to intptr_t; use separate array for 8-bit counters

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@281845 91177308-0d34-0410-b5e6-96231b3b80d8