add external dependencies in a pre-built way to avoid incompatibilities

external/include/sodium/crypto_stream_xchacha20.h

@@ -0,0 +1,61 @@
+#ifndef crypto_stream_xchacha20_H
+#define crypto_stream_xchacha20_H
+
+/*
+ *  WARNING: This is just a stream cipher. It is NOT authenticated encryption.
+ *  While it provides some protection against eavesdropping, it does NOT
+ *  provide any security against active attacks.
+ *  Unless you know what you're doing, what you are looking for is probably
+ *  the crypto_box functions.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include "export.h"
+
+#ifdef __cplusplus
+# ifdef __GNUC__
+#  pragma GCC diagnostic ignored "-Wlong-long"
+# endif
+extern "C" {
+#endif
+
+#define crypto_stream_xchacha20_KEYBYTES 32U
+SODIUM_EXPORT
+size_t crypto_stream_xchacha20_keybytes(void);
+
+#define crypto_stream_xchacha20_NONCEBYTES 24U
+SODIUM_EXPORT
+size_t crypto_stream_xchacha20_noncebytes(void);
+
+#define crypto_stream_xchacha20_MESSAGEBYTES_MAX SODIUM_SIZE_MAX
+SODIUM_EXPORT
+size_t crypto_stream_xchacha20_messagebytes_max(void);
+
+SODIUM_EXPORT
+int crypto_stream_xchacha20(unsigned char *c, unsigned long long clen,
+                            const unsigned char *n, const unsigned char *k)
+            __attribute__ ((nonnull));
+
+SODIUM_EXPORT
+int crypto_stream_xchacha20_xor(unsigned char *c, const unsigned char *m,
+                                unsigned long long mlen, const unsigned char *n,
+                                const unsigned char *k)
+            __attribute__ ((nonnull));
+
+SODIUM_EXPORT
+int crypto_stream_xchacha20_xor_ic(unsigned char *c, const unsigned char *m,
+                                   unsigned long long mlen,
+                                   const unsigned char *n, uint64_t ic,
+                                   const unsigned char *k)
+            __attribute__ ((nonnull));
+
+SODIUM_EXPORT
+void crypto_stream_xchacha20_keygen(unsigned char k[crypto_stream_xchacha20_KEYBYTES])
+            __attribute__ ((nonnull));
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif