buildkernel without INET6 blows up trying to build if_gif module

make buildkernel blows a gasket when trying to build the if_gif module
if the kernel config file doesn't have the INET6 option:

===> if_gif (all)
cc -O2 -fno-strict-aliasing -pipe -Werror -D_KERNEL -DKLD_MODULE -nostdinc -I-   -DHAVE_KERNEL_OPTION_HEADERS -include /usr/obj/usr/src/sys/UP_ATAPICAM/opt_global.h -I. -I_at_ -I_at_/contrib/altq -I_at_/../include -finline-limit=8000 -fno-common -g -I/usr/obj/usr/src/sys/UP_ATAPICAM -mno-align-long-strings -mpreferred-stack-boundary=2  -mno-mmx -mno-3dnow -mno-sse -mno-sse2 -mno-sse3 -ffreestanding -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -fformat-extensions -std=c99 -c /usr/src/sys/modules/if_gif/../../net/if_gif.c
cc -O2 -fno-strict-aliasing -pipe -Werror -D_KERNEL -DKLD_MODULE -nostdinc -I-   -DHAVE_KERNEL_OPTION_HEADERS -include /usr/obj/usr/src/sys/UP_ATAPICAM/opt_global.h -I. -I_at_ -I_at_/contrib/altq -I_at_/../include -finline-limit=8000 -fno-common -g -I/usr/obj/usr/src/sys/UP_ATAPICAM -mno-align-long-strings -mpreferred-stack-boundary=2  -mno-mmx -mno-3dnow -mno-sse -mno-sse2 -mno-sse3 -ffreestanding -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -fformat-extensions -std=c99 -c /usr/src/sys/modules/if_gif/../../netinet/in_gif.c
cc -O2 -fno-strict-aliasing -pipe -Werror -D_KERNEL -DKLD_MODULE -nostdinc -I-   -DHAVE_KERNEL_OPTION_HEADERS -include /usr/obj/usr/src/sys/UP_ATAPICAM/opt_global.h -I. -I_at_ -I_at_/contrib/altq -I_at_/../include -finline-limit=8000 -fno-common -g -I/usr/obj/usr/src/sys/UP_ATAPICAM -mno-align-long-strings -mpreferred-stack-boundary=2  -mno-mmx -mno-3dnow -mno-sse -mno-sse2 -mno-sse3 -ffreestanding -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -fformat-extensions -std=c99 -c /usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: `in6_gif_input' undeclared here (not in a function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: initializer element is not constant
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: (near initialization for `in6_gif_protosw.pr_input')
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: `rip6_output' undeclared here (not in a function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: initializer element is not constant
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: (near initialization for `in6_gif_protosw.pr_output')
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: `rip6_ctloutput' undeclared here (not in a function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: initializer element is not constant
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:79: error: (near initialization for `in6_gif_protosw.pr_ctloutput')
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:83: error: `rip6_usrreqs' undeclared here (not in a function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:83: error: initializer element is not constant
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:83: error: (near initialization for `in6_gif_protosw.pr_usrreqs')
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:87: warning: function declaration isn't a prototype
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c: In function `in6_gif_output':
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:92: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:148: error: invalid application of `sizeof' to incomplete type `ip6_hdr' 
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:149: error: invalid application of `sizeof' to incomplete type `ip6_hdr' 
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:150: error: invalid application of `sizeof' to incomplete type `ip6_hdr' 
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:157: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:158: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:158: error: `IPV6_VERSION_MASK' undeclared (first use in this function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:158: error: (Each undeclared identifier is reported only once
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:158: error: for each function it appears in.)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:159: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:159: error: `IPV6_VERSION' undeclared (first use in this function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:160: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:161: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:162: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:162: error: `ip6_gif_hlim' undeclared (first use in this function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:163: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:166: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:173: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:174: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:183: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:184: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:185: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:192: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:193: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:194: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:218: warning: implicit declaration of function `ip6_output'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:218: warning: nested extern declaration of `ip6_output'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:218: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:222: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:223: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:224: error: structure has no member named `gif_ro6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c: At top level:
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:232: warning: function declaration isn't a prototype
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c: In function `in6_gif_input':
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:247: error: `ip6stat' undeclared (first use in this function)
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:258: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c: In function `gif_validate6':
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:333: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:334: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:347: error: dereferencing pointer to incomplete type
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c: At top level:
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:374: warning: function declaration isn't a prototype
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c: In function `gif_encapcheck6':
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:379: error: storage size of 'ip6' isn't known
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:379: warning: unused variable `ip6'
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c: At top level:
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:395: warning: function declaration isn't a prototype
/usr/src/sys/modules/if_gif/../../netinet6/in6_gif.c:406: warning: function declaration isn't a prototype
*** Error code 1

Stop in /usr/src/sys/modules/if_gif.
*** Error code 1

Stop in /usr/src/sys/modules.
*** Error code 1

Stop in /usr/obj/usr/src/sys/UP_ATAPICAM.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.