priv: Add discard_const macros.

include/libssh/priv.h

@@ -278,6 +278,25 @@ SSH_PACKET_CALLBACK(ssh_packet_kexdh_init);
 /** Overwrite the complete string with 'X' */
 #define BURN_STRING(x) do { if ((x) != NULL) memset((x), 'X', strlen((x))); } while(0)
 
+/**
+ * This is a hack to fix warnings. The idea is to use this everywhere that we
+ * get the "discarding const" warning by the compiler. That doesn't actually
+ * fix the real issue, but marks the place and you can search the code for
+ * discard_const.
+ *
+ * Please use this macro only when there is no other way to fix the warning.
+ * We should use this function in only in a very few places.
+ *
+ * Also, please call this via the discard_const_p() macro interface, as that
+ * makes the return type safe.
+ */
+#define discard_const(ptr) ((void *)((uintptr_t)(ptr)))
+
+/**
+ * Type-safe version of discard_const
+ */
+#define discard_const_p(type, ptr) ((type *)discard_const(ptr))
+
 #ifdef HAVE_LIBGCRYPT
 /* gcrypt_missing.c */
 int my_gcry_dec2bn(bignum *bn, const char *data);