sparc: fix for missing include file

[David Miller]

From: Andreas Schwab <schwab@linux-m68k.org>
Date: Sat, 13 Dec 2014 21:43:14 +0100

> David Miller <davem@davemloft.net> writes:
> 
>> The destination is not necessarily NULL terminated,
> 
> This is strn*cat*, the destination must be a string.  Otherwise, what
> would strlen (s1) be?

Indeed, thanks for the clarification.