r308090: buildkernel failure: undefined reference to ...

Most recent r308090 fails to buildkernel with lots of " undefined reference to ...",
as shown below. 

[...]
Building /usr/obj/usr/src/sys/THOR/kernel.full
linking kernel.full
refcount.o:(.data+0x8): undefined reference to `sysctl___vfs_zfs'
freebsd32_misc.o: In function `freebsd32_utimes':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1255: undefined reference to
`kern_utimesat' freebsd32_misc.o: In function `freebsd32_lutimes':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1277: undefined reference to `kern_lutimes'
freebsd32_misc.o: In function `freebsd32_futimes':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1298: undefined reference to `kern_futimes'
freebsd32_misc.o: In function `freebsd32_futimesat':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1319: undefined reference to
`kern_utimesat' freebsd32_misc.o: In function `freebsd32_futimens':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1341: undefined reference to
`kern_futimens' freebsd32_misc.o: In function `freebsd32_utimensat':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1362: undefined reference to
`kern_utimensat' freebsd32_misc.o: In function `freebsd32_lseek':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1489: undefined reference to `sys_lseek'
freebsd32_misc.o: In function `freebsd32_truncate':

[...]


/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1504: undefined reference to `sys_truncate'
freebsd32_misc.o: In function `freebsd32_getdirentries':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1548: undefined reference to
`kern_getdirentries' freebsd32_misc.o: In function `freebsd32_stat':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1778: undefined reference to `kern_statat'
freebsd32_misc.o: In function `freebsd32_fstatat':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1844: undefined reference to `kern_statat'
freebsd32_misc.o: In function `freebsd32_lstat':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:1860: undefined reference to `kern_statat'
freebsd32_misc.o: In function `freebsd32_posix_fallocate':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:2992: undefined reference to
`kern_posix_fallocate' freebsd32_misc.o: In function `freebsd32_posix_fadvise':
/usr/src/sys/compat/freebsd32/freebsd32_misc.c:3003: undefined reference to
`kern_posix_fadvise'
[...]


kern_descrip.o: In function `_fdrop':
/usr/src/sys/kern/kern_descrip.c:2908: undefined reference to `M_FADVISE'
/usr/src/sys/kern/kern_descrip.c:2908: undefined reference to `M_FADVISE'
/usr/src/sys/kern/kern_descrip.c:2908: undefined reference to `M_FADVISE'
/usr/src/sys/kern/kern_descrip.c:2908: undefined reference to `M_FADVISE'
/usr/src/sys/kern/kern_descrip.c:2908: undefined reference to `M_FADVISE'
kern_descrip.o:/usr/src/sys/kern/kern_descrip.c:2908: more undefined references to
`M_FADVISE' follow kern_descrip.o: In function `sys_nfstat':

[...]

/usr/src/sys/kern/vfs_bio.c:1216: undefined reference to `sys_sync'
vfs_cache.o:(.data+0x8): undefined reference to `sdt_provider_vfs'
vfs_cache.o:(.data+0xf8): undefined reference to `sdt_provider_vfs'
vfs_cache.o:(.data+0x1b8): undefined reference to `sdt_provider_vfs'
vfs_cache.o:(.data+0x248): undefined reference to `sdt_provider_vfs'
vfs_cache.o:(.data+0x338): undefined reference to `sdt_provider_vfs'
vfs_cache.o:(.data+0x3c8): more undefined references to `sdt_provider_vfs' follow
vfs_extattr.o: In function `sys_extattr_set_fd':
/usr/src/sys/kern/vfs_extattr.c:229: undefined reference to `getvnode'

[...]
/usr/src/sys/ufs/ffs/ffs_alloc.c:3102: undefined reference to `getvnode'
vnode_if.o:(.data+0x38): undefined reference to `sdt_provider_vfs'
vnode_if.o:(.data+0xf8): undefined reference to `sdt_provider_vfs'
vnode_if.o:(.data+0x228): undefined reference to `sdt_provider_vfs'
vnode_if.o:(.data+0x2e8): undefined reference to `sdt_provider_vfs'
vnode_if.o:(.data+0x418): undefined reference to `sdt_provider_vfs'
vnode_if.o:(.data+0x4d8): more undefined references to `sdt_provider_vfs' follow
*** Error code 1