Add missing include to fix the build with recent GCCs.

Include <string.h> so that the definitions for memcpy() and friends
can be found. Fixes the build with GCC 4.6.3, at least.

Reviewed-by: Andreas Pakulat
REVIEW: 104926
(cherry picked from commit f3e0daaba7a9afdd3c01a7a2fd258f523c4f48d0)