[sanitizer] speed up the bitvector-based deadlock detector by ~15% (iterate over the currently held locks using the array, not the bitvector. Bitvector is not the best data structure to iterate over)

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@205168 91177308-0d34-0410-b5e6-96231b3b80d8