[diff.mods.to.definitions] Add entry for 'nullptr_t in stddef.h'

Author: tkoeppe

source/compatibility.tex

@@ -2295,6 +2295,13 @@
 
 Subclause \ref{cwchar.syn} describes the changes.
 
+\pnum
+Headers \tcode{<cstddef>}~(\ref{cstddef.syn})\indexlibrary{\idxhdr{cstddef}}
+and \tcode{<stddef.h>}\indexlibrary{\idxhdr{stddef.h}} declare the name
+\tcode{nullptr_t} (respectively in namespace \tcode{std} and in the
+global namespace) in addition to the names declared in \tcode{<stddef.h>}
+in the C standard library.
+
 \rSec2[diff.mods.to.behavior]{Modifications to behavior}
 
 \pnum