libFuzzer trunk doesn't build with clang-3.8 anymore

[attekett]

$ docker-compose build libfuzzer-base
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Step 6 : RUN mkdir /src /work && cd /src && git clone https://chromium.googlesource.com/chromium/llvm-project/llvm/lib/Fuzzer && clang++ -c -g -O2 -std=c++11 Fuzzer/.cpp -IFuzzer && ar ruv libFuzzer.a Fuzzer.o && mkdir -p /work/libfuzzer && mv libFuzzer.a /usr/local/lib && rm *.o && rm -rf Fuzzer
---> Running in ba768abc1e98
Cloning into 'Fuzzer'...
Fuzzer/FuzzerTracePC.cpp:193:3: error: use of undeclared identifier '__sanitizer_dump_coverage'
__sanitizer_dump_coverage(PCs, GetNumPCs());
^
1 error generated.

We have to change clang to a newer version, or checkout libFuzzer @ 34a77f5afc4efc03323a70e4f68b092f36f8a89b