[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 the phases of translation produce.

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

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

Author: AlisdairM

source/basic.tex

@@ -2649,23 +2649,10 @@
 only namespace names are considered.%
 \indextext{lookup!name|)}%
 
-\rSec1[basic.link]{Program and linkage}%
+\rSec1[basic.link]{Linkage}%
 \indextext{linkage|(}
 
 \pnum
-\indextext{program}%
-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 can have
 \defnadj{external}{linkage},
 \defnadj{module}{linkage},

source/intro.tex

@@ -476,7 +476,7 @@
 \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\iref{module.unit}.
 \end{defnote}
 
 \definition{required behavior}{defns.required.behavior}

source/lex.tex

@@ -24,6 +24,11 @@
 
 \rSec1[lex.separate]{Separate translation}
 
+\pnum
+\indextext{program}%
+A \defn{program} consists of one or more translation units\iref{lex.phases,module.unit}
+linked together.
+
 \pnum
 \indextext{conventions!lexical|(}%
 \indextext{compilation!separate|(}%

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}
@@ -26,6 +30,10 @@
     module-name-qualifier identifier \terminal{.}
 \end{bnf}
 
+\pnum
+\indextext{translation unit}%
+A translation unit consists of a sequence of declarations.
+
 \pnum
 A \defn{module unit} is a translation unit that contains
 a \grammarterm{module-declaration}.