Add futimes, futimesat, and lutimes.

Spotted these while cleaning up <sys/cdefs.h> --- if we remove __USE_XOPEN2K8,
libchrome decides you "must" have futimes. Adding the missing functions (all
just alternative interfaces to utimensat(2) system call) lets us clean up
without breaking anything.

Change-Id: If44fab08ee3de0e31066d650d128a3c96323529b