gas: respect CR_EOL also for scrubbing

While apparently intended to be only externally controlled (e.g. via
specifying CFLAGS at make invocation), we should still keep scrubber and
lexer in sync in this regard. There's one place which imo was previously
wrong already, but would go further wrong and hence is being adjusted
right here: An .mri directive can be terminated by any kind of "line"
(really: statement) separators.