bcm53xx. Should have mentioned that before.
This tree not contain adopted patches for bcm53xx. If you want build vanilla 4.12 - move two patches
0000-revert-mtd-nand-Remove-unused-chip--write_page-hook.patch and 0001-fix-net-phy-swconfig-for-4.12.patch from target/linux/ramips/patches-4.12/ to target/linux/generic/patches-4.12/ and rebuild kernel.
will give it a shot
Those patches did get rid of the compilation errors. However, I'm seeing kernel panics. I'll just wait until someone more capable than me tries this. Thanks!!
Finally rebased this work after https://git.lede-project.org/74d00a8c and renamed the branch from linux-4.12 to kernel. Link updated in initial post.