DFSan-based fuzzer (proof of concept).

Summary:
This adds a simple DFSan-based (i.e. taint-guided) fuzzer mutator,
see the comments for details.

Test Plan: a test added

Reviewers: samsonov, pcc

Reviewed By: samsonov, pcc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8669

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233613 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Fuzzer/FuzzerDriver.cpp

@@ -161,6 +161,7 @@ int FuzzerDriver(int argc, char **argv, UserCallback Callback) {
   Options.UseCounters = Flags.use_counters;
   Options.UseFullCoverageSet = Flags.use_full_coverage_set;
   Options.UseCoveragePairs = Flags.use_coverage_pairs;
+  Options.UseDFSan = Flags.dfsan;
   Options.PreferSmallDuringInitialShuffle =
       Flags.prefer_small_during_initial_shuffle;
   if (Flags.runs >= 0)