Fix sim-eng build.

Missing a <string.h> header.

git cherry-pick -e d0019991

Change-Id: I7a3dc7cb7d2855fde56512b3dcb181a092055497
diff --git a/tests/nusensors/nusensors.cpp b/tests/nusensors/nusensors.cpp
index 29e2069..9d1a90c 100644
--- a/tests/nusensors/nusensors.cpp
+++ b/tests/nusensors/nusensors.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <string.h>
 #include <stdint.h>
 #include <string.h>
 #include <sys/cdefs.h>