Drop support for GCC 4.x?

PR2231 caused a lot of build errors on a nightly machine with GCC 4.8.4. GCC 4.8.4 does not seem to support C++11 well enough for the latest GTest to compile.

Should we upgrade the compiler on this machine and say that ITK requires GCC 5.x and later? Correspondingly update ITKSoftwareGuide. Or maybe revert the PR?

So far, @hjmjohnson supported updating compiler requirements in a private email exchange.

CentOS 7’s default compiler is GCC 4.8.5. It will have full updates until 2020-08-06. I am currently running nightly valgrind and coverages for ITK on this OS. And use it for SimpleITK CI with a variety of different compilers. However, with the change in direction of CentOS, another Linux distribution will likely be used in the near future.

Redhat 7 is corresponding version for CentOS 7 also has GCC 4.8.5. Redhat is rather notorious for long enterprise support. It use used on all the cluster I work with. Redhat 7 EOL date is 6/30/2024.

I do not propose we support the compiler until this date, but it is a sensible upper bound in this discussion.

It would be nice to have a table to common Linux distro’s, gcc versions and EOL dates. I don’t have time to continue the search. This would provide some additional reasoning for the change is supported compilers on a minor change of the toolkit.

Dropping less than (but not) 4.8.5 would not cause a problem with anything I am using right now.

*EDIT: Dzenan pointed out that the valgrind and coverage builds are failing on the dashboard.

I see that Valgrind build runs into the same errors. So revert PR2231?

Having this type of braking change occurring after the second release candidate for 5.2 is not be expected.

So certainly for 5.2, IMHO.

Sounds good. So after 5.2.0 final we will bump both minimum CMake version and minimum GCC version.