This PR is upstreaming changes in the Seraphis lib here: https://github.com/UkoeHB/monero/pull/39. This header adds a macro `VA_ARGS_COMMAPREFIX`
which, when passed `__VA_ARGS__`, expands to `, __VA_ARGS__` unless the length of `__VA_ARGS__` is 0, in which case it expands to nothing. This
macro is useful for passing/declaring optional function arguments.
