CWG3112 Introduce a term for C-style variadic functions

Fixes NB FR 155 (C++26 CD).

Author: eisenwave

source/declarations.tex

@@ -3874,6 +3874,10 @@
 \end{codeblock}
 \end{example}
 
+\pnum
+A function with a parameter-type-list that has an ellipsis
+is termed a \defnadj{vararg}{function}.
+
 \pnum
 An \defn{explicit-object-parameter-declaration} is
 a \grammarterm{parameter-declaration} with a \keyword{this} specifier.