OK I found the culprit. It's the fsverity-utils repo here: https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/fsverity-utils.git/
Commit: 5cd90ca608770 ("Introduce libfsverity") Which added the following line to the Makefile is causing this build failure: $(call cc-option,-Wimplicit-fallthrough) \ -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1882167 Title: ubuntu_zfs_xfs_generic failed to build on X-4.4 Status in linux package in Ubuntu: Incomplete Bug description: The test compilation will fail with: cc: error: unrecognized command line option '-Wimplicit-fallthrough' This build issue does not exist with 4.4.0-180 + gcc 5.4.0-6ubuntu1~16.04.12 Please find attachment for the full build log. ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: linux-image-4.4.0-181-generic 4.4.0-181.211 ProcVersionSignature: Ubuntu 4.4.0-181.211-generic 4.4.223 Uname: Linux 4.4.0-181-generic s390x NonfreeKernelModules: zfs zunicode zcommon znvpair zavl AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access '/dev/snd/': No such file or directory AplayDevices: Error: [Errno 2] No such file or directory: 'aplay' ApportVersion: 2.20.1-0ubuntu2.23 Architecture: s390x ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord' CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found. CurrentDmesg: Date: Thu Jun 4 22:56:00 2020 HibernationDevice: RESUME=/dev/mapper/mpatha1 IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig' Lspci: Lsusb: Error: command ['lsusb'] failed with exit code 1: PciMultimedia: ProcFB: Error: [Errno 2] No such file or directory: '/proc/fb' ProcKernelCmdLine: root=/dev/mapper/kernel01_vg-kernel01_lv crashkernel=196M BOOT_IMAGE=0 RelatedPackageVersions: linux-restricted-modules-4.4.0-181-generic N/A linux-backports-modules-4.4.0-181-generic N/A linux-firmware 1.157.23 RfKill: Error: [Errno 2] No such file or directory: 'rfkill' SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1882167/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp