Import code from previous AssetBuilder version

thirdparty/libtomcrypt/stream/chacha/chacha_done.c

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+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ */
+
+#include "tomcrypt.h"
+
+#ifdef LTC_CHACHA
+
+/**
+  Terminate and clear ChaCha state
+  @param st      The ChaCha state
+  @return CRYPT_OK on success
+*/
+int chacha_done(chacha_state *st)
+{
+   LTC_ARGCHK(st != NULL);
+   XMEMSET(st, 0, sizeof(chacha_state));
+   return CRYPT_OK;
+}
+
+#endif
+
+/* ref:         HEAD -> master, tag: v1.18.2 */
+/* git commit:  7e7eb695d581782f04b24dc444cbfde86af59853 */
+/* commit time: 2018-07-01 22:49:01 +0200 */