Rationale (June, 2014):

EWG should determine the desired outcome for this question.

[This suggestion was adopted as paper P2156R1 at the June, 2021 plenary.]

The standard attributes noreturn, carries_dependency, and deprecated all specify that they cannot appear more than once in an attribute-list, but there is no such prohibition if they appear in separate attribute-specifiers within a single attribute-specifier-seq. Since intuitively these cases are equivalent, they should be treated the same, accepting duplicates in both or neither.