Roll libFuzzer to uptake minimizer improvements.

https://chromium.googlesource.com/chromium/llvm-project/llvm/lib/Fuzzer/+log/b9454401d..57ed38604

TBR=ochang@chromium.org,kcc@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2776003002
Cr-Commit-Position: refs/heads/master@{#459640}
1 file changed