[lex.separate][module.unit] move definitions of program and translation unit

The definition of program at the top of [basic.link] should move to
the front of [lex.separate] so that it is defined before its first
usage, and also clarifies that is what the phases of translation produce.

Similarly, move the definition of the grammar production translation-unit
to the top of the only clause whose grammar actually uses it, [module.unit].

Finally, retitle [basic.link] as just Linkage, rather than
Programs and linkage.

Author: AlisdairM

source/basic.tex

@@ -2870,24 +2870,10 @@
 \end{note}
 \indextext{splice|)}
 
-\rSec1[basic.link]{Program and linkage}%
+\rSec1[basic.link]{Linkage}%
 \indextext{linkage|(}
 
 \pnum
-\indextext{program}%
-\indextext{linking}%
-A \defn{program} consists of one or more translation units\iref{lex.separate}
-linked together. A translation unit consists
-of a sequence of declarations.
-
-\begin{bnf}
-\nontermdef{translation-unit}\br
-    \opt{declaration-seq}\br
-    \opt{global-module-fragment} module-declaration \opt{declaration-seq} \opt{private-module-fragment}
-\end{bnf}
-
-\pnum
-\indextext{translation unit}%
 A name has
 \defnadj{external}{linkage},
 \defnadj{module}{linkage},

source/intro.tex

@@ -494,7 +494,7 @@
 \begin{defnote}
 Only one definition for such a function is in effect for the duration of the program's
 execution, as the result of creating the program\iref{lex.phases} and resolving the
-definitions of all translation units\iref{basic.link}.
+definitions of all translation units.
 \end{defnote}
 
 \definition{required behavior}{defns.required.behavior}

source/lex.tex

@@ -27,8 +27,13 @@
 \pnum
 \indextext{conventions!lexical|(}%
 \indextext{compilation!separate|(}%
+\indextext{program}%
+A \defn{program} consists of one or more translation units\iref{lex.phases}
+linked together.
 The text of the program is kept in units called
 \defnx{source files}{source file} in this document.
+
+\pnum
 A source file together with all the headers\iref{headers}
 and source files included\iref{cpp.include} via the preprocessing
 directive \tcode{\#include}, less any source lines skipped by any of the
@@ -40,7 +45,7 @@
 \begin{note}
 A \Cpp{} program need not all be translated at the same time.
 Translation units can be separately translated and then later linked
-to produce an executable program\iref{basic.link}.
+to produce an executable program.
 \end{note}
 \indextext{compilation!separate|)}
 
@@ -174,7 +179,7 @@
 Whitespace characters separating tokens are no longer significant.
 The resulting tokens constitute a \defn{translation unit} and
 are syntactically and
-semantically analyzed as a \grammarterm{translation-unit}\iref{basic.link} and
+semantically analyzed as a \grammarterm{translation-unit}\iref{module.unit} and
 translated.
 \begin{note}
 The process of analyzing and translating the tokens can occasionally
@@ -200,8 +205,8 @@
 \end{note}
 \begin{note}
 Previously translated translation 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,
+The separate translation units of a program communicate by (for example)
+calls to functions whose identifiers have external or module linkage\iref{basic.link},
 manipulation of objects whose identifiers have external or module linkage, or
 manipulation of data files.
 \end{note}

source/modules.tex

@@ -6,6 +6,10 @@
 \rSec1[module.unit]{Module units and purviews}
 
 \begin{bnf}
+\nontermdef{translation-unit}\br
+    \opt{declaration-seq}\br
+    \opt{global-module-fragment} module-declaration \opt{declaration-seq} \opt{private-module-fragment}
+
 \nontermdef{module-declaration}\br
     \opt{export-keyword} module-keyword module-name \opt{module-partition} \opt{attribute-specifier-seq} \terminal{;}
 \end{bnf}