Options on where to run and how to build for (Ubuntu) Linux on s390x

  1. Launchpad PPAs

Launchpad offers so called Personal Package Archives (PPAs) that allow to package and compile for different architectures. By default PPAs build for x86 and amd64 - other architectures need to be explicitly enabled.
First create a Launchpad account: https://login.launchpad.net/+new_account
Sign the Ubuntu code of conduct (that’s required to activate PPAs): https://launchpad.net/codeofconduct
Activate/create a PPA: https://launchpad.net/people/+me/

1 - Personal package archives - PPA

And fill out the fields with the (PPA) name and description:

Once the PPA is created:

Select ‘Change details’.

At the edit (PPA) dialog:

Scroll down to the bottom of the page where all supported architectures are listed:

Finally select the architecture(s) you want the PPA to be compiled and build for.
A GPG key need to be registered with your Launchpad account to be able to upload: https://help.launchpad.net/Packaging/PPA/Uploading

Further references: