Currently we add -O2 in the lit.cfg for libFuzzer: https://github.com/llvm-mirror/compiler-rt/blob/master/test/fuzzer/lit.cfg#L74
However, the latest revision of the patch by Matt [which originally added that line] did not have that in the latest iteration (https://reviews.llvm.org/D44798).
It looks like it crept in as a result of a merge conflict, and should be dropped.