[yocto] NooB: applying new patches to older files, where do I find the older files?

[R]

Hello List,

First I'm working on a unsupported distro (Manjaro) and try to get an 
older version (2.7.1) of poky working. I have ask a question before and 
Ross Burton pointed me in the direction of a patch.
Now I'm trying to apply that patch, however the patch is for a newer 
version of the original files, so I need to make my own patch for the 
older version of these files.
(reason: WARNING: Some of the context lines in patches were ignored. 
This can lead to incorrectly applied patches.)

The patch says: the file to be patch is e.g. /linux-user/syscall.c
My question is where can I find the original syscall.c before any 
patches are applied to it?

Just to be complete: I have tried the latest warrior branch and that 
worked fine. My objective is not just to get it working be also to get a 
grip on how the system works :-)

Thanks,
Robert.