That paper isn't relevant here. From the paper (emphasis added): > 7.1.3 Reserved Identifiers > [snip] > Macro names and identifiers with external linkage th

That paper isn't relevant here. From the paper (emphasis added): > 7.1.3 Reserved Identifiers > [snip] > Macro names and identifiers with external linkage that are specified in the C standard library clauses. > This proposal does not propose any changes to these reserved identifiers. Furthermore, that paper doesn't make the use of reserved external identifiers not UB, so there's no change there either.