Remove IWYU

[knelli2]

Proposed changes

This never really worked that well for us and we've had it disabled for a while now. I don't think we'll be trying to revive it again so I'm just removing it.

Upgrade instructions

Removed include-what-you-use (IWYU) as a dependency.

Code review checklist

• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.
• The PR lists upgrade instructions and is labeled bugfix or
  new feature if appropriate.

Further comments

[nilsdeppe]

🎉 Thanks for doing this :D

[knelli2]

Umm GCC is unhappy and I'm not really sure why...

Edit: Oh I think it's the PCH.

[wthrowe]

I agree, it looks like the PCH didn't rebuild properly for some reason, but I don't see an obvious cause.

Otherwise, this looks good.

[knelli2]

Let's see if a rebase fixes things.

Edit: Sad...it did not...

[wthrowe]

My guess is you've hit some inconsistency in how ccache and gcc (for pragma once) decide that a header is unchanged. Try making some change to TMPL.hpp that isn't just comments or add a blank line or something to change line numbers.

[wthrowe]

Looks like it's compiling now.

[knelli2]

@wthrowe @nilsdeppe clang-tidy timed out because there were too many changed files, however, I noticed we were only running it on 1 core, so I added a commit to run it on 4 cores and we'll see if that helps. Otherwise just a rebase.

Edit: Looks like clang tidy still failed. This time I think -j4 caused it to run out of memory with so many files.

[wthrowe]

Let's drop the commit that crashed clang-tidy. I'm not worried about the timeout on a PR like this.