Parse a statement_or_null into a vl-stmt, which is possible since we allow a vl-nullstmt as a vl-stmt.
(vl-parse-statement-or-null &key (tokstream 'tokstream) (config 'config)) → (mv errmsg? value new-tokstream)
This is the same in both Verilog-2005 and SystemVerilog-2012:
statement_or_null ::= statement | {attribute_instance} ';'