Upgrade LLVM to version 8

clang-7 cannot build zlib-ng, since it thinks that

    typedef unsigned int uv4si __attribute__((vector_size(16)));
    typedef vector unsigned int uv4si;

are different types. clang-8 does not have this issue.

Signed-off-by: Ilya Leoshkevich <[email protected]>

Author: iii-i

docker/image/Dockerfile

@@ -34,7 +34,7 @@ ENV DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && \
     apt-get install -y ca-certificates curl
 COPY fs/ /
-ARG llvm_version=7
+ARG llvm_version=8
 RUN apt-get update && \
     apt-get install --no-install-recommends --yes \
         binutils-multiarch \