ToT build failure with ToT GCC (strncpy warning)

[Joseph Myers]

Please see the discussion starting 
<https://sourceware.org/ml/libc-alpha/2017-11/msg00336.html> and help with 
the review (if you agree with the analysis at 
<https://sourceware.org/ml/libc-alpha/2017-11/msg00388.html> then a 
corresponding patch to fix the bug described there is needed, as we don't 
currently have one).

-- 
Joseph S. Myers
joseph@codesourcery.com