Fix "error: 'strlen' was not declared in this scope".

Change-Id: I8ae39a6b3cf4844429e6211b3c909c6f72978832
diff --git a/include/hardware/qemu_pipe.h b/include/hardware/qemu_pipe.h
index 814b20b..53aec97 100644
--- a/include/hardware/qemu_pipe.h
+++ b/include/hardware/qemu_pipe.h
@@ -23,6 +23,7 @@
 #include <pthread.h>  /* for pthread_once() */
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 #include <errno.h>
 
 #ifndef D