ARROW-4340: [C++][CI] Build IWYU for LLVM 7 in iwyu docker-compose job

Following the instructions in docker-compose.yml gives me a working IWYU build now

```
export PYTHON_VERSION=3.6
docker-compose build cpp
docker-compose build python
docker-compose build lint
docker-compose run iwyu
```

Author: François Saint-Jacques <[email protected]>
Author: Wes McKinney <[email protected]>

Closes #3643 from wesm/ARROW-4340 and squashes the following commits:

56733fc <François Saint-Jacques> Refactor iwyu build into docker install script. (#8)
e1c46c7 <Wes McKinney> Build IWYU for LLVM 7 in iwyu docker-compose job

ci/docker_install_iwyu.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+set -eu
+
+: ${IWYU_REPO:="https://github.com/include-what-you-use/include-what-you-use.git"}
+: ${IWYU_BRANCH:="clang_7.0"}
+: ${IWYU_SRC:="/tmp/iwyu"}
+: ${IWYU_HOME:="/opt/iwyu"}
+
+git clone "${IWYU_REPO}" "${IWYU_SRC}"
+git -C "${IWYU_SRC}" checkout ${IWYU_BRANCH}
+
+mkdir -p "${IWYU_HOME}"
+pushd "${IWYU_HOME}"
+
+# Build IWYU for current Clang
+export CC=clang-7
+export CXX=clang++-7
+
+cmake -DCMAKE_PREFIX_PATH=/usr/lib/llvm-7 "${IWYU_SRC}"
+make -j4
+
+popd

dev/lint/Dockerfile

@@ -18,15 +18,17 @@
 FROM arrow:python-3.6
 
 RUN apt-get install -y -q gnupg && \
-    apt update && \
+    apt-get update && \
     apt-get install -y -q \
       clang-7 \
+      libclang-7-dev \
       clang-format-7 \
       clang-tidy-7 \
       clang-tools-7
 
 RUN conda install flake8 && \
     conda clean --all -y
 
-# https://bugs.launchpad.net/ubuntu/+source/iwyu/+bug/1769334
-RUN ln -sv /usr/lib/clang/6.0 /usr/lib/clang/5.0.1
+ENV PATH=/opt/iwyu/bin:$PATH
+ADD ci/docker_install_iwyu.sh /arrow/ci/
+RUN arrow/ci/docker_install_iwyu.sh

dev/lint/run_iwyu.sh

@@ -16,19 +16,21 @@
 # limitations under the License.
 #
 
+set -eux
+
 export ARROW_BUILD_TOOLCHAIN=$CONDA_PREFIX
 
 mkdir -p /build/lint
 pushd /build/lint
 
 cmake -GNinja \
+      -DARROW_FLIGHT=ON \
+      -DARROW_GANDIVA=ON \
       -DARROW_PARQUET=ON \
       -DARROW_PYTHON=ON \
       -DCMAKE_CXX_FLAGS='-D_GLIBCXX_USE_CXX11_ABI=0' \
       -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
       /arrow/cpp
-# Make so that vendored bits are built
-ninja arrow_shared
 
 popd
 

docker-compose.yml

@@ -207,9 +207,6 @@ services:
     #   docker-compose build lint
     #   docker-compose run iwyu
     image: arrow:lint
-    environment:
-      CC: clang
-      CXX: clang++
     command: arrow/dev/lint/run_iwyu.sh
     volumes: *ubuntu-volumes