The Signal Converted to a Return Status routine converts any
    signaled condition value to a value returned as a function. The
    signaled condition is returned to the caller of the user routine
    that established the handler that is calling LIB$SIG_TO_RET. This
    routine may be established as or called from a condition handler.

    Format

      LIB$SIG_TO_RET  signal-arguments ,mechanism-arguments