/usr/include/sys/types.h:62: error: conflicting types for ‘dev_t’
/usr/include/linux/types.h:13: error: previous declaration of ‘dev_t’ was here
/usr/include/sys/types.h:67: error: conflicting types for ‘gid_t’
/usr/include/linux/types.h:27: error: previous declaration of ‘gid_t’ was here
/usr/include/sys/types.h:72: error: conflicting types for ‘mode_t’
/usr/include/linux/types.h:15: error: previous declaration of ‘mode_t’ was here
/usr/include/sys/types.h:77: error: conflicting types for ‘nlink_t’
/usr/include/linux/types.h:16: error: previous declaration of ‘nlink_t’ was here
/usr/include/sys/types.h:82: error: conflicting types for ‘uid_t’
/usr/include/linux/types.h:26: error: previous declaration of ‘uid_t’ was here

解法

CFLAGS += $(addprefix -idirafter,$(KERNEL_DIR)/include)

内核目录作为第二查找目录