Move a declaration that's private to libcrypto

Don't expose purely libcrypto internal symbols, even to libssl.
Reviewed-by: NMatt Caswell <matt@openssl.org>

crypto/include/internal/err_int.h

+/*
+ * Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the OpenSSL licenses, (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * https://www.openssl.org/source/license.html
+ * or in the file LICENSE in the source distribution.
+ */
+
+#ifndef INTERNAL_ERR_INT_H
+# define INTERNAL_ERR_INT_H
+
+void err_load_crypto_strings_int(void);
+
+#endif

crypto/init.c

@@ -67,6 +67,7 @@
 #include <internal/engine.h>
 #include <internal/comp.h>
 #include <internal/err.h>
+#include <internal/err_int.h>
 #include <internal/objects.h>
 #include <stdlib.h>
 #include <assert.h>

include/internal/err.h

@@ -58,7 +58,6 @@
 #ifndef INTERNAL_ERR_H
 # define INTERNAL_ERR_H
 
-void err_load_crypto_strings_int(void);
 void err_free_strings_int(void);
 
 #endif