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

external/include/sodium/crypto_core_salsa20.h

@@ -0,0 +1,36 @@
+#ifndef crypto_core_salsa20_H
+#define crypto_core_salsa20_H
+
+#include <stddef.h>
+#include "export.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define crypto_core_salsa20_OUTPUTBYTES 64U
+SODIUM_EXPORT
+size_t crypto_core_salsa20_outputbytes(void);
+
+#define crypto_core_salsa20_INPUTBYTES 16U
+SODIUM_EXPORT
+size_t crypto_core_salsa20_inputbytes(void);
+
+#define crypto_core_salsa20_KEYBYTES 32U
+SODIUM_EXPORT
+size_t crypto_core_salsa20_keybytes(void);
+
+#define crypto_core_salsa20_CONSTBYTES 16U
+SODIUM_EXPORT
+size_t crypto_core_salsa20_constbytes(void);
+
+SODIUM_EXPORT
+int crypto_core_salsa20(unsigned char *out, const unsigned char *in,
+                        const unsigned char *k, const unsigned char *c)
+            __attribute__ ((nonnull(1, 2, 3)));
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif