Add a few missing headers

Fixes build with gcc 4.3.2

Signed-off-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
diff --git a/tools/aidl/options.h b/tools/aidl/options.h
index dc3c45a..e7e62ec 100644
--- a/tools/aidl/options.h
+++ b/tools/aidl/options.h
@@ -1,6 +1,7 @@
 #ifndef DEVICE_TOOLS_AIDL_H
 #define DEVICE_TOOLS_AIDL_H
 
+#include <string.h>
 #include <string>
 #include <vector>