There's a merged pull request on the void-packages repository

linux4.19/5.1/5.2: build with ELFv2 ABI on ppc64 big endian
https://github.com/void-linux/void-packages/pull/13064
Description: This adds patches to build the kernel as ELFv2 binaries for big endian ppc64, just like is default for little endian. While IBM does not officially support this and the upstream is not interested in it (because of the former), it has some mainly performance benefits (on unrelated note, we build all big endian userland as ELFv2 also, which IBM does not support either, but musl requires it and glibc at least allows it).

I tested this on a Power Mac G5 as well as in a virtual machine and it seems to be working very nicely. It's also a small patch that shouldn't conflict with anything much ever and is trivlal to redo or even ditch if needed (userland ABI does not affect kernel ABI or the other way around), it also fixes the GCC 9.1 build by side effect (as `-mcall-aixdesc` is no longer necessary).

@pullmoll / @stenstorp, mind giving this a spin also? I think it's worth a try at least. From my side there's still some stuff to confirm, so consider WIP for now, though I'm not expecting any changes to be necessary.