Who broke world and how to fix?

Updating uname -a
FreeBSD 11.0-ALPHA5 FreeBSD 11.0-ALPHA5
#3 r302248: Tue Jun 28 10:11:31 PDT 2016
data/obj/usr/src/sys/SPEW  amd64

to top-of-tree

===> lib/libsbuf (obj,all,install)
cc   -O2 -pipe   -MD  -MF.depend.subr_prf.o -MTsubr_prf.o -std=gnu99 \
-fstack-protector-strong -Wsystem-headers -Werror -Wall -Wno-format-y2k \
-W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes \
-Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch \
 -Wshadow -Wunused-parameter -Wcast-align -Wchar-subscripts -Winline \
-Wnested-externs -Wredundant-decls -Wold-style-definition \
-Wno-pointer-sign -Wmissing-variable-declarations -Wthread-safety \
-Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable  \
-Qunused-arguments  -c /usr/src/lib/libsbuf/../../sys/kern/subr_prf.c \
-o subr_prf.o
/usr/src/lib/libsbuf/../../sys/kern/subr_prf.c:1209:7: error: implicit
 declaration of function 'atomic_cmpset_int' is invalid in C99
 [-Werror,-Wimplicit-function-declaration]
                if (atomic_cmpset_int(counter, c, c - 1)) {
                    ^

-- 
Steve