Annex C (informative) Compatibility [diff]

C.6 C standard library [diff.library]

C.6.2 Modifications to definitions [diff.mods.to.definitions]

C.6.2.5 Header <stdalign.h> [diff.header.stdalign.h]

The token alignas is a keyword in this International Standard ([lex.key]).
It does not appear as a macro name defined in <cstdalign> ([depr.cstdalign.syn]).