commit https://git.zx2c4.com/WireGuard/commit/?id=799895f27f3d63d2e92a5c1c411205ae70f2a5ca
breaks out of tree module build on arm64 , kernel 5.1.10
strangely when building x86_64 everything is fine

  CC [M]  /home/asavah/kross/src/WireGuard/src/main.o
In file included from /home/asavah/kross/src/WireGuard/src/compat/compat.h:824,
                 from <command-line>:
./include/linux/timekeeping.h:67:8: error: unknown type name ‘ktime_t’
   67 | extern ktime_t ktime_get(void);
      |        ^~~~~~~

The following patch fixes the issue, however I have no idea why x86_64
builds fine and arm64 does not,
neither I'm sure that the patch is right, it fixed the issue for me tho.