Sorry for random Cc: list.
v2.6.24-rc1-423-g97855b4, with CONFIG_HEADERS_CHECK=y
$ make
...
CHECK include/linux/tipc_config.h
/home/raa/linux/usr/include/linux/tipc_config.h requires linux/string.h, which does not exist in exported headers
make[3]: *** [/home/raa/linux/usr/include/linux/.check.tipc_config.h] Error 1
make[2]: *** [linux] Error 2
make[1]: *** [headers_check] Error 2
make: *** [vmlinux] Error 2
-