Use Alpine as base for docker build environment

build-docker-image.sh

 #!/bin/bash
 set -e
 pushd docker
-docker build -t bpftrace-builder -f Dockerfile.ubuntu .
+docker build -t bpftrace-builder -f Dockerfile.alpine .
 popd

docker/Dockerfile.alpine

+FROM alpine:3.8
+RUN apk add --update \
+  bison \
+  build-base \
+  clang-dev \
+  clang-static \
+  cmake \
+  elfutils-dev \
+  flex-dev \
+  git \
+  linux-headers \
+  llvm5-dev \
+  llvm5-static \
+  zlib-dev
+
+# Put LLVM directories where CMake expects them to be
+RUN ln -s /usr/lib/cmake/llvm5 /usr/lib/cmake/llvm
+RUN ln -s /usr/include/llvm5/llvm /usr/include/llvm
+RUN ln -s /usr/include/llvm5/llvm-c /usr/include/llvm-c
+
+COPY build.sh /build.sh
+ENTRYPOINT ["/bin/sh", "/build.sh"]