yea you are right it should be <linux/errno.h>
please forgive as i bat about more non helpfull things
but the real thing that bothers me is
Entering directory `/usr/src/linux-headers-2.6.12-9-386'
might be a distribution thing but
the only thing i know with the word headers in it is
/lib/modules/`uname -r` needs to be the actual directory used to compile your currently running kernel
almost always just named linux-x.y.x unless you changed its name for some reason