Buildworld fails if WITHOUT_INET6=YES defined

cc -target i386-unknown-freebsd12.0 --sysroot=/usr/obj/usr/src/tmp -
B/usr/obj/usr/src/tmp/usr/bin  -O2 -pipe -march=core2  -DHAVE_CONFIG_H -
I/usr/src/lib/libpcap -I/usr/obj/usr/src/lib/libpcap -
D_U_="__attribute__((unused))" -DHAVE_SNPRINTF -DHAVE_VSNPRINTF -
DBUILDING_PCAP -DHAVE_NET_PFVAR_H -I/usr/src/contrib/libpcap -MD  -
MF.depend.fad-getad.o -MTfad-getad.o -std=gnu99 -fstack-protector-strong -Wno-
pointer-sign -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -
Wno-tautological-compare -Wno-unused-value -Wno-parentheses-equality -Wno-
unused-function -Wno-enum-conversion -Wno-unused-local-typedef -Wno-switch -
Wno-switch-enum -Wno-knr-promoted-parameter -Wno-parentheses  -Qunused-
arguments  -c /usr/src/contrib/libpcap/fad-getad.c -o fad-getad.o
cc -target i386-unknown-freebsd12.0 --sysroot=/usr/obj/usr/src/tmp -
B/usr/obj/usr/src/tmp/usr/bin  -O2 -pipe -march=core2  -DHAVE_CONFIG_H -
I/usr/src/lib/libpcap -I/usr/obj/usr/src/lib/libpcap -
D_U_="__attribute__((unused))" -DHAVE_SNPRINTF -DHAVE_VSNPRINTF -
DBUILDING_PCAP -DHAVE_NET_PFVAR_H -I/usr/src/contrib/libpcap -MD  -
MF.depend.gencode.o -MTgencode.o -std=gnu99 -fstack-protector-strong -Wno-
pointer-sign -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -
Wno-tautological-compare -Wno-unused-value -Wno-parentheses-equality -Wno-
unused-function -Wno-enum-conversion -Wno-unused-local-typedef -Wno-switch -
Wno-switch-enum -Wno-knr-promoted-parameter -Wno-parentheses  -Qunused-
arguments  -c /usr/src/contrib/libpcap/gencode.c -o gencode.o
/usr/src/contrib/libpcap/gencode.c:695:9: error: no member named 'ai' in 
'struct _compiler_state'
        cstate.ai = NULL;
        ~~~~~~ ^
/usr/src/contrib/libpcap/gencode.c:4916:13: error: use of undeclared 
identifier 'cstate'
                bpf_error(cstate, "direction applied to 'gateway'");
                          ^
/usr/src/contrib/libpcap/gencode.c:4923:11: error: use of undeclared 
identifier 'cstate'
                switch (cstate->linktype) {
                        ^
/usr/src/contrib/libpcap/gencode.c:4961:17: error: use of undeclared 
identifier 'cstate'
                b1 = gen_host(cstate, **alist++, 0xffffffff, proto, Q_OR, 
Q_HOST);
                              ^
/usr/src/contrib/libpcap/gencode.c:4963:19: error: use of undeclared 
identifier 'cstate'
                        tmp = gen_host(cstate, **alist++, 0xffffffff, proto, 
Q_OR,
                                       ^
/usr/src/contrib/libpcap/gencode.c:4972:12: error: use of undeclared 
identifier 'cstate'
        bpf_error(cstate, "illegal modifier of 'gateway'");
                  ^
6 errors generated.
*** Error code 1

Stop.
make[5]: stopped in /usr/src/lib/libpcap
*** Error code 1