The tree is built as a libretro core and nothing else, so the
standalone frontends lose their lanes: the Visual Studio and UWP
solutions, the Android app, iOS, the macOS app bundle, the AppImage
and the manual packaging workflows. PPSSPPHeadless and
PPSSPPUnitTest stay, built as named targets so a configure no longer
pulls the SDL frontend in, and keep feeding the headless, frametest,
qemu and Alpine jobs; the Docker image builds the same way.
Two lanes cover builds nothing ran before: the core on an arm64 host,
and the CMake build of the core on Linux.