Fix itk/5.1.2 with cpp20

[fdgStilla]

Fix #19418

---

• I've read the contributing guidelines.
• I've used a recent Conan client version close to the currently deployed.
• I've tried at least one configuration locally with the conan-center hook activated.

[uilianries]

@fdgStilla Thank you for your backport, but I see ITK offers new releases (RC) with these patches incorporated already.

I would ask to not try backporting it, but add a new version instead. So, who needs to use >=C++17 should include an official version already patched to support C++20.

https://github.com/InsightSoftwareConsortium/ITK/tags

https://github.com/InsightSoftwareConsortium/ITK/blob/v5.4rc02/Modules/Core/Common/include/itkThreadPool.h

[fdgStilla]

Can we add release candidate to conan?

[uilianries]

Can we add release candidate to conan?

Yes. It's not encouraged because we will have a temporary release which will be available for few time and occupy not only Conan Ceneter, but require CI resource to be built. Same for alpha and beta versions.

However, some projects delay many months between each release, so providing RC is fine. We just don't recommend bumping version for each RC in case they are not really used by users.

[AbrilRBS]

Closing in favour of adding the recently released 5.4 version, will do so in the following days. Thanks a lot for your patience in this one :)