ruby2.7-dev: extensions fails to build on ppc64el by lack of gcc-10

Attached is the debdiff. A matching package has been uploaded to my PPA: https://launchpad.net/~schopin/+archive/ubuntu/test-ppa/+sourcepub/12853681/+listing-archive-extra

In the same PPA you'll find the ruby-mysql2 package that was the initial reason I looked into this, and it now builds fine :)

Thanks for the patch Simon! I'd change a bit your proposed solution here, I'd add g++-10 [ppc64el] to Recommends instead of gcc-10 [ppc64el] to Depends. Let's use g++-10 to follow what doko did in the Build-Depends, I am not sure but maybe we can find an extension which requires a C++ compiler and then we will have the same issue. And I'd prefer Recommends to avoid forcing any user to install the entire GCC toolchain in case they opt-out. Would you mind applying those changes?

Moreover, I am seeing in your PPA that the ruby2.7 build on arm64 failed:

https://launchpad.net/~schopin/+archive/ubuntu/test-ppa/+build/22344486

It seems a timeout issue and it might be fixed with a simple rebuild. Could you confirm that to us before we upload the package?

I purposefully chose gcc-10 instead of g++-10 as, while the ruby implementation seems to use C++ internally, the exposed headers and ABI are C. If you insist I'll change it.

I don't think Recomends is a good way to go as I believe sbuild doesn't take them into account, which sort of defeats the purpose here ;-). However to be sure I've uploaded a version with Recommends gcc-10 to my PPA, let's see how it goes.

Trying out the Recommends change on the PPA does trigger the failure, so we need to use Depends. The new build succeeded for arm64 but failed for armhf, with a similar failure mode (timeouts). Retrying it now.

I mistakenly added impish as a target series. I misread my build reports in my PPA, sorry about that! Marking it as invalid there.

I am not sure if I understood your point here Simon, at the moment Impish and Jammy have the same ruby2.7 version. Are you saying the ruby-mysql2 build worked fine in one and failed in the other?

It seems so, yes. See
https://launchpad.net/~schopin/+archive/ubuntu/rebuilds/+packages

I believe it's because GCC 10 is included in the builder chroots for
impish, but not for jammy. You can see gcc-10 being upgraded in the logs
for the impish build.

So, the bug doesn't appear on impish on our builders, but mostly by
happenstance.

I'm uploading this workaround for jammy. It helps to fix ftbfs for packages which build both python and ruby bindings.