Could not find valid clang executable at clang (2019.3.x-linux-il2cpp)

[mob-sakai]

Bug description

When I start a Unity project on unityci/editor:2019.3.*-linux-il2cpp-0, it exits with compilation errors.

stdout:
il2cpp.exe didn't catch exception: System.InvalidOperationException: C++ code builder is unable to build C++ code for Linux: Could not find valid clang executable at clang
  at Unity.IL2CPP.Building.CppProgramBuilder.ThrowIfCannotBuildInCurrentEnvironment () [0x00051] in <248b4a691c5d4e1b965d90f17ea422c0>:0 
  at Unity.IL2CPP.Building.CppProgramBuilder.Build (Unity.IL2CPP.Building.Statistics.IBuildStatistics& statistics) [0x00001] in <248b4a691c5d4e1b965d90f17ea422c0>:0 
  at Unity.IL2CPP.Building.Statistics.BuildingTestRunnerHelper.BuildAndLogStatsForTestRunner (Unity.IL2CPP.Building.CppProgramBuilder builder, Unity.IL2CPP.Building.Statistics.IBuildStatistics& statistics) [0x00001] in <248b4a691c5d4e1b965d90f17ea422c0>:0 
  at il2cpp.Program.DoRun (System.String[] args, System.Collections.Generic.List`1[T] foundAssemblies) [0x005bc] in <3d7b04f5e89e4d189194b279bc8abf31>:0 
  at il2cpp.Program.Run (System.String[] args, System.Boolean setInvariantCulture) [0x00042] in <3d7b04f5e89e4d189194b279bc8abf31>:0 
  at il2cpp.Program.Main (System.String[] args) [0x00002] in <3d7b04f5e89e4d189194b279bc8abf31>:0 
...

• Tested with Add test workflow #60 (in my repo): https://github.com/mob-sakai/docker/runs/1724887604?check_suite_focus=true

How to reproduce

1. Run the following command:

UNITY_LICENSE_FILE=<YOUR_ULF_PATH>
docker run --rm -v "$(pwd)":/logs -i unityci/editor:2019.3.14f1-linux-il2cpp-0 bash <<EOF
echo "==== Activate"
echo '$(cat $UNITY_LICENSE_FILE)' > ulf
unity-editor -logFile /logs/activate.log -quit -nographics -manualLicenseFile ulf

echo "==== Get a simple project for test (IL2CPP)"
wget https://github.com/game-ci/docker/files/5833152/test.tar.gz
tar -xvf test.tar.gz

echo "==== Add dependencies (#61: add python build-essential clang)"
apt-get -q update && apt-get -q install -y python build-essential clang

echo "==== Build"
unity-editor -logFile /logs/build.log -quit -nographics -projectPath reference-project-test -buildLinux64Player Build
EOF

2. See build.log

Expected behavior

Compilation completed successfully.

Additional details

2019.3.x-linux-il2cpp requires IL2CPP_ADDITIONAL_ARGS='--sysroot-path=/ --tool-chain-path=/' to build with il2cpp.

• https://forum.unity.com/threads/unity-2019-3-linux-il2cpp-player-can-only-be-built-with-linux-error.822210/#post-5633977
• Tested with Add test workflow #60 (in my repo): https://github.com/mob-sakai/docker/runs/1724891391?check_suite_focus=true