[lex.separate] Redistribute second comment

The second comment in [lex.separate] is both too specific, and not specific
enough.  Move the last sentence about use of separately translated TUs to
the end of the first note, where it seems most appropriate.  Move the rest
of the note to the end of translation phase 8, where we are in a position
to talk about preserving the separately translated TUs *and instantiation units*
for linking in phase 9.

Author: AlisdairM

source/lex.tex

@@ -39,19 +39,8 @@
 called a \defnadj{preprocessing}{translation unit}.
 \begin{note}
 A \Cpp{} program need not all be translated at the same time.
-\end{note}
-
-\pnum
-\begin{note}
-Previously translated translation units and instantiation
-units can be preserved individually or in libraries. The separate
-translation units of a program communicate\iref{basic.link} by (for
-example)
-calls to functions whose identifiers have external or module linkage,
-manipulation of objects whose identifiers have external or module linkage, or
-manipulation of data files. Translation units can be separately
-translated and then later linked to produce an executable
-program\iref{basic.link}.
+Translation units can be separately translated and then later linked to
+produce an executable program\iref{basic.link}.
 \end{note}
 \indextext{compilation!separate|)}
 
@@ -240,6 +229,15 @@
 \end{note}
 The
 program is ill-formed if any instantiation fails.
+\begin{note}
+Previously translated translation units and instantiation
+units can be preserved individually or in libraries. The separate
+translation units of a program communicate\iref{basic.link} by (for
+example)
+calls to functions whose identifiers have external or module linkage,
+manipulation of objects whose identifiers have external or module linkage, or
+manipulation of data files.
+\end{note}
 
 \item All external entity references are resolved. Library
 components are linked to satisfy external references to