The /usr/src/libc/syscall/ directory no longer exists.

Instead, they files you need to modify are in the libc/sysdeps/linux/ directory. If your system call only works on one architecture, then you need to use the architecture-dependent subdirectories i386 and m68k (at present; that will soon expand to at least sparc, and maybe other platforms).

If you need to know more, please ask more...