stable 4.16.5 hmm build error

From: Randy Dunlap
Date: Thu Apr 26 2018 - 17:52:38 EST

kernel/fork.o: In function `__mmdrop':
/kernel/build_kernel/linux-4.16.4/kernel/fork.c:600: undefined reference to `hmm_mm_destroy'

"It is also reproduced in linux-4.16.5"

There have been a few attempts to fix this build error. The kernel mainline
repo seems to have it fixed, but it looks to me like Arnd's latest patch
(9d8a463a7016e: "mm/hmm: fix header file if/else/endif maze, again")
was mis-merged to 4.16.5 stable.

Please take a look. Do you already have a fixup for this?