[PATCH 2/4] rust: Use error_operand_p in rust-gcc.cc

Just a simple cleanupof the code to use error_operand_p instead of directly comparing against error_mark_node. This also moves some cdoe around when dealing with error_operand_p just to be faster and/or slightly tighten up the code slightly. gcc/rust/ChangeLog: * rust-gcc.cc (Bvariable::

[PATCH 2/4] rust: Use error_operand_p in rust-gcc.cc

Just a simple cleanupof the code to use error_operand_p instead of directly comparing against error_mark_node. This also moves some cdoe around when dealing with error_operand_p just to be faster and/or slightly tighten up the code slightly. gcc/rust/ChangeLog: * rust-gcc.cc (Bvariable::