[lex.comment] Move the subclause earlier, to where it better fits

Comments should fit betweem character sets (to define the basic source
character set) and preprocessor tokens, that must already understand
comments in order to treat them as whitespace.

Author: AlisdairM

source/lex.tex

@@ -467,6 +467,29 @@
 None of these names or aliases have leading or trailing spaces.
 \end{note}
 
+\rSec1[lex.comment]{Comments}
+
+\pnum
+\indextext{comment|(}%
+\indextext{comment!\tcode{/*} \tcode{*/}}%
+\indextext{comment!\tcode{//}}%
+The characters \tcode{/*} start a comment, which terminates with the
+characters \tcode{*/}. These comments do not nest.
+\indextext{comment!\tcode{//}}%
+The characters \tcode{//} start a comment, which terminates immediately before the
+next new-line character. If there is a form-feed or a vertical-tab
+character in such a comment, only whitespace characters shall appear
+between it and the new-line that terminates the comment; no diagnostic
+is required.
+\begin{note}
+The comment characters \tcode{//}, \tcode{/*},
+and \tcode{*/} have no special meaning within a \tcode{//} comment and
+are treated just like other characters. Similarly, the comment
+characters \tcode{//} and \tcode{/*} have no special meaning within a
+\tcode{/*} comment.
+\end{note}
+\indextext{comment|)}
+
 \rSec1[lex.pptoken]{Preprocessing tokens}
 
 \indextext{token!preprocessing|(}%
@@ -681,29 +704,6 @@
 \end{note}
 \indextext{token|)}
 
-\rSec1[lex.comment]{Comments}
-
-\pnum
-\indextext{comment|(}%
-\indextext{comment!\tcode{/*} \tcode{*/}}%
-\indextext{comment!\tcode{//}}%
-The characters \tcode{/*} start a comment, which terminates with the
-characters \tcode{*/}. These comments do not nest.
-\indextext{comment!\tcode{//}}%
-The characters \tcode{//} start a comment, which terminates immediately before the
-next new-line character. If there is a form-feed or a vertical-tab
-character in such a comment, only whitespace characters shall appear
-between it and the new-line that terminates the comment; no diagnostic
-is required.
-\begin{note}
-The comment characters \tcode{//}, \tcode{/*},
-and \tcode{*/} have no special meaning within a \tcode{//} comment and
-are treated just like other characters. Similarly, the comment
-characters \tcode{//} and \tcode{/*} have no special meaning within a
-\tcode{/*} comment.
-\end{note}
-\indextext{comment|)}
-
 \rSec1[lex.header]{Header names}
 
 \indextext{header!name|(}%