$ cd /root/poc3296 && sh build.sh
(guest: DragonFly dfbsd 6.5-DEVELOPMENT #0 X86_64_GENERIC, cc = DragonFly clang)
$ cc -O2 -Wall -o trigger_changeaddr trigger_changeaddr.c
(no diagnostics, exit 0)

fix-validation builds:
$ cc -O2 -Wall -o fixcheck fixcheck.c
fixcheck.c:28:3: warning: implicit declaration of function 'exit' [-Wimplicit-function-declaration] (cosmetic; missing <stdlib.h>)
(exit 0)

patched module build (in-guest, /usr/src/sys/net/pf):
$ cd /usr/src && patch -p0 < /root/fix.diff
Patching file sys/net/pf/pf_ioctl.c using Plan A...
Hunk #1 succeeded at 2311.  Hunk #2 succeeded at 2340.  done
$ make obj && make
[... cc -O2 -D_KERNEL -Werror -DKLD_MODULE ... pf_osfp.c pf_subr.c pf_table.c pf_ruleset.c]
cc -Wl,--build-id=sha1 -nostdlib -Wl,--hash-style=sysv -r -Wl,-d -o pf.ko if_pflog.o if_pfsync.o pf.o pf_if.o pf_ioctl.o pf_norm.o pf_osfp.o pf_subr.o pf_table.o pf_ruleset.o
(exit 0, -Werror clean) -> /usr/obj/usr/src/sys/net/pf/pf.ko (350392 bytes)