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

external/include/sodium/randombytes_sysrandom.h

@@ -0,0 +1,19 @@
+
+#ifndef randombytes_sysrandom_H
+#define randombytes_sysrandom_H
+
+#include "export.h"
+#include "randombytes.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+SODIUM_EXPORT
+extern struct randombytes_implementation randombytes_sysrandom_implementation;
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif