Attempt to fix USE_SYSTEM_ITK

[melrobin]

With this commit I was able to get the ITK Software Guide to build with the setting USE_SYSTEM_ITK=ON.

[jhlegarreta]

Thanks for the contribution @melrobin 💯. Have not tested.

An in-line comment and a few comments about the commit style:

• Please, use the established commit prefixes to allow a clean and helpful commit history:
  https://github.com/InsightSoftwareConsortium/ITKSoftwareGuide/blob/master/CONTRIBUTING.md#contributing-patches-with-git-and-github

  Configuring this pre-commit hook will be helpful for that prupose:
  https://github.com/InsightSoftwareConsortium/ITKSoftwareGuide/blob/master/Utilities/Hooks/commit-msg

  This involves splitting changes with different purposes (e.g. 5ef2d9a).

• Also, provide a full description of the rationale behind the change in the commit message body. This allows people to know the existing failure or bug and how the fix addresses it.

Adopting these procedures allows maintainers and people that will read the commits afterwards have a clear view of what was changed, and what motivated such changes.

This also applies to the PR message when multiple commits are involved.

Although this certainly involves more work for the contributor, and potentially dealing with more PRs for maintainers, it is an effort that pays off. Additionally, this has the benefit that some PRs that do not require strict testing (e.g. typos) can be merged almost immediately, and reduces the number of essential and critical changes to review in PRs that require strict testing.

Thanks again. Keep up the good work.

[dzenanz]

Please squash the fix-related commits into one, and have a separate commit for the typo.

[dzenanz]

@jhlegarreta we should clean up this TODO, as many/most things have been done by now.

[jhlegarreta]

@dzenanz I agree the list needs to be cleaned up, each item be checked, and maybe issues be opened instead of keeping this file. Not sure if I will have the bandwidth in the short-, mid-term to do this though.

[dzenanz]

Turning the entire file into issues is a great idea! We don't have to address them soon.

[dzenanz]

I meant to comment, not approve yet.

[dzenanz]

Looks good on a glance.

[jhlegarreta]

Looks good. Thanks for pushing this Hans. Builds have been succeeding, so I guess we will need to figure out the way to make it succeed here before merging.

You may want to add the NumFOCUS copyright notice to the newly added Python script.

[thewtex]

Thank you @melrobin @hjmjohnson @jhlegarreta !

[jhlegarreta]

Have not tried this locally, and I am unsure whether the current changes fulfill the aim of the initial PR (building the SW guide with a system ITK), but I guess these changes are useful/necessary going forward, so approving.

Adding the copyright header to the newly added Python script can done in a separate PR to avoid further delays to these changes.