ARROW-1413: [C++] Add include-what-you-use configuration

[fjetter]

This adds iwyu make target to run include-what-you-use on all changed files of the current branch. As suggested in the ticket https://issues.apache.org/jira/browse/ARROW-1413 I took the code of apache-kudu as a starting point and added a few modifications.

While it works fine locally, I'm struggling to get it to work (i.e. build is failing) on travis. Somehow the check isn't performed without raising an error. I expect that clang doesn't have the iwyu properly installed but I couldn't verify it, yet.

Also, the tool requires a compile_commands.json to be present including all the files to be checked which is why I added the export CMAKE_EXPORT_COMPILE_COMMANDS=1 to the travis_env_common.sh
This may be an issue since we are partially compiling multiple times but never the full codebase which is why I included the make/ninja iwyu twice.

[wesm]

I don't think it's necessary to run this on every build in Travis as it will primarily inflate our build times, only that we do a manual cleanup periodically (e.g. a couple times a release cycle)

[wesm]

@fjetter can you capitalize the "Arrow" in the PR title (and add hyphen so it reads "ARROW-1413:")? I will take this for a spin when I can and then merge, sometime in the next couple days

[xhochy]

I took this for a spin and I'm not really sure this produces the expected results. At least we need to tune the iwyu configuration a lot.

[wesm]

We definitely should not be applying automated changes. iwyu does require a ton of tuning

[fjetter]

@wesm I'd remove the travis stuff again or do you want to keep it? Currently it doesn't do anything.

[wesm]

Can you remove it ("ninja iwyu", etc.) from the Travis scripts for now?

[wesm]

Forgot I have push permissions on your fork, I can take it from here

[wesm]

+1. I will wait for the build to pass

[fjetter]

@wesm if you want to invoke it on the whole code base you can simply add cmake -DCMAKE_CXX_INCLUDE_WHAT_YOU_USE=iwyu <iwyu args> to the cmake arguments. It takes care for you of the compilation database and prints the output of iwyu to stdout

c.f. https://cmake.org/cmake/help/v3.9/prop_tgt/LANG_INCLUDE_WHAT_YOU_USE.html?highlight=include

For including it in the build chain, though, I would've preferred a partial check.

[wesm]

I see. I wanted an easy option to run with the filters and suppressions. The option to do a partial run as with Kudu is still there (omit the "all" option from iwyu.sh). We can continue to tweak this as we venture forward, this is by no means final. Just want to get us all in the habit of keeping our includes clean