spl 0.6.5.10 (and possibly other versions) fail to build with GCC 7.1.0. One possible solution is to remove the -Werror compiler flag which causes a warning to be treated as an error. Another solution is to apply commit https://github.com/zfsonlinux/spl/commit/4f8e643afe9d8cc558566e1dda05ef597cb2526e which prevents the warning from occurring.
Created attachment 478922 [details, diff]
patch to apply the above mentioned commit to 0.6.5.10
Thanks for reporting. Currently Richard Yao and I are discussing which solution to go with. I think we most likely will apply the patch that's in upstream (Which seems to be also what you have attached).
I just pushed zfs 0.6.5.11 to the tree. This upstream release includes GCC 7.1 build fixes. Please try that version (in about 30 minutes+) and let us know if it works for you.