If one will try to build -CURRENT on 10-stable, he will get:

o)
===> rescue/rescue/chown/tests (depend)
(cd /ssd/never/head/usr.sbin/chown/tests && make -f /ssd/never/head/usr.sbin/chown/tests/Makefile SUBDIR= _RECURSING_PROGS=  depend)
cc  -O2 -pipe -march=nocona  -DRESCUE -std=gnu99 -fstack-protector -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 /ssd/never/head/usr.sbin/chown/chown.c
MAKEOBJDIRPREFIX=/ssd/never/obj/ssd/never/head/rescue/rescue make -f rescue.mk exe
cc  -O2 -pipe -march=nocona  -c rescue.c
rescue.c:59:2: warning: implicit declaration of function 'crunched_usage' is invalid in C99 [-Wimplicit-function-declaration]
        crunched_usage();
        ^
1 warning generated.
echo "int _crunched_cat_stub(int argc, char **argv, char **envp){return main(argc,argv,envp);}" >cat_stub.c
cc  -O2 -pipe -march=nocona  -c cat_stub.c
cat_stub.c:1:67: warning: implicit declaration of function 'main' is invalid in C99 [-Wimplicit-function-declaration]
int _crunched_cat_stub(int argc, char **argv, char **envp){return main(argc,argv,envp);}
                                                                  ^
1 warning generated.
make[5]: don't know how to make /ssd/never/obj/ssd/never/head/rescue/rescue//ssd/never/head/bin/cat/cat.o. Stop