Update chapters/functions.tex

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/functions.tex

@@ -2374,8 +2374,7 @@ \subsection{Annotations for External Functions}\label{annotations-for-external-l
 
   The included code should be valid C89 code.
   If the \lstinline[language=grammar]!external-function-call! contains any `size`-expression, the tool is responsible for ensuring that a C-header defining \lstinline[language=C]!size_t! is included before the \lstinline!"insertedCode"!.
-This gives a code fragment \lstinline!"insertedCode"! conditionally preceded by a header for \lstinline[language=C]!size_t!.
-It must be possible to compile this code fragment separately.
+The \lstinline!"insertedCode"!, conditionally preceded by a header for \lstinline[language=C]!size_t!, must be a valid translation unit.
 
   When an \lstinline!Include! annotation is present, it shall provide a prototype for the external function, and hence the tool shall not produce an automatically generated prototype in the generated code in this case.