BEL character is delivered to the user and then all pending error messages in the current error context
are delivered using a call to ERR_FLUSH. On successful completion, the error context is annulled and
STATUS reset to SAI__OK.
If no error messages have been reported in the current error context, a warning message is generated
but no error results.
If an error occurs during output of the error messages, the error context is not annulled and STATUS is
returned set to ERR__OPTER.
CALL ERR_FLBEL( STATUS )
The global status: it is set to SAI__OK on return if the error message output is
successful; if not, it is set to ERR__OPTER.