I've posted it on Bug Tracker. I want to work on the bug but I have been unable to find the source code for these functions.
On the same website as the bug tracker, there is a 'Source code' menu at the top. that will provide instructions to either clone the source repository using Mercurial, or just browse the source code via the website.
to determine what file contains the code of interest, you can use
octave:2> which strncmp
'strncmp' is a built-in function from the file libinterp/corefcn/strfns.cc