Hm, this is strange, the source shouldn't be altered at all if you dont run ./autogen.sh manually. Did you try to do this as root? If not, could you try it as root, and as root in /root/ to see if this a permission issue?
If not, and if you used my previous kernel packages, please build a new kernel first with the new scripts....the old ones were not that great...because of this whole libc idiot move I did...
Jup, just checked, this is libc relates...the log states it already...please drop my old kernel and build a new 4.1.15 with the script (btrfs will be fine without the tools until you build and add them)