add obsolete futimesat()

this function is obsolete, however it's available as a syscall
and as such qemu userspace emulation tries to forward it to the
host kernel.

src/stat/futimesat.c

@@ -0,0 +1,9 @@
+#include <sys/time.h>
+#include "syscall.h"
+
+#ifdef SYS_futimesat
+int futimesat(int dirfd, const char *pathname, const struct timeval times[2])
+{
+	return syscall(SYS_futimesat, dirfd, pathname, times);
+}
+#endif