Well, firstly, you are in the wrong place for such a question. You probably should subscribe to the linux kernel mailing list. Go to www.kernel.org
and scroll down a bit. You will find instructions for subscribing.
Second, when you change the arch includes in your linux kernel source tree, this does not change the includes in your /usr/include tree - nor should it. Nor can you casually change those files, or you potentially break any other build that doesn't know about your changes to the ABI.
Just curious, why do you want to add a syscall?