Annex G (informative) Ill-formed, no diagnostic required [ifndr]

G.6 [dcl]: Declarations [ifndr.dcl]

G.6.9[ifndr:dcl.attr.noreturn.trans.unit.mismatch]
Specified in: [dcl.attr.noreturn]

1
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No diagnostic is required if a function is declared in one translation unit with the noreturn attribute but has declarations in other translation units without the attribute.
2
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[Example 1: 

Translation unit #1:[[noreturn]] void f() {}

Translation unit #2:void f(); // IFNDR, declared without noreturn — end example]