libmincrypt: suppress warning messages

- deal with implict declaration issue
- deal with some -Wunused issues

Change-Id: I253f1412a696c4811ade70a931fb1c01b31c62a5
diff --git a/libmincrypt/dsa_sig.c b/libmincrypt/dsa_sig.c
index 8df6cf7..101314b 100644
--- a/libmincrypt/dsa_sig.c
+++ b/libmincrypt/dsa_sig.c
@@ -26,6 +26,7 @@
 
 #include <string.h>
 
+#include "mincrypt/dsa_sig.h"
 #include "mincrypt/p256.h"
 
 /**