Bug 255509

On 21st of April, Ubuntu 20.04 will go out of support:

https://trac.webkit.org/wiki/WebKitGTK/DependenciesPolicy

On that day, it will be possible to upgrade minimum dependencies of GCC and GStreamer. Dependencies will be upgraded to the minimum shipped version of the next OS in line, which is Debian 11. In other words, GCC will be upgraded to GCC10.2 and GStreamer will be upgraded to version 1.18.4.

We still would like to extend Ubuntu 20.04 support for a while more, since its user base is still big. We have two post-commit bots that build WPE and WebKitGTK packages for Ubuntu 20.04 using the minimal modules dependencies:

  - [GTK-Linux-64bit-Release-Packaging-Nightly-Ubuntu2004](https://build.webkit.org/#/builders/30)
  - [WPE-Linux-64bit-Release-Packaging-Nightly-Ubuntu2004](https://build.webkit.org/#/builders/2)

These bots will need to get their GCC version upgraded (GCC10 is distributed as a system package for Ubuntu 20.04) as well as their GStreamer packages. Unfortunately, Ubuntu 20.04 doesn't provide packages for GStreamer 1.18.4 and I was not either able to locate any PPA backports. Thus, it seems reasonable to add the new GStreamer dependencies to JHBuild minimal modules, so we can still build WPE and WebKitGTK packages for Ubuntu 20.04.