[config.tex] Create and apply macro to denote last core chapter

This PR should show no difference in the rendered document, but
will make it much easier to refactor the Core clauses in the
future --- just as we can refactor Library clauses today.

Author: AlisdairM

source/config.tex

@@ -8,6 +8,10 @@
 %% Release date
 \newcommand{\reldate}{\today}
 
+%% Core chapters
+\newcommand{\firstcorechapter}{lex}
+\newcommand{\lastcorechapter}{cpp}
+
 %% Library chapters
 \newcommand{\firstlibchapter}{support}
 \newcommand{\lastlibchapter}{exec}

source/expressions.tex

@@ -7552,7 +7552,7 @@
 
 \item
 an operation that would have undefined or erroneous behavior
-as specified in \ref{intro} through \ref{cpp},
+as specified in \ref{intro} through \ref{\lastcorechapter},
 excluding \ref{dcl.attr.assume} and \ref{dcl.attr.noreturn};
 \begin{footnote}
 This includes,

source/intro.tex

@@ -256,7 +256,7 @@
 Implementations are allowed, but not required,
 to diagnose it\iref{intro.compliance.general}.
 Evaluation of a constant expression\iref{expr.const}
-never exhibits behavior specified as erroneous in \ref{intro} through \ref{cpp}.
+never exhibits behavior specified as erroneous in \ref{intro} through \ref{\lastcorechapter}.
 \end{defnote}
 
 \definition{expression-equivalent}{defns.expression.equivalent}
@@ -644,7 +644,7 @@
 issuance of a diagnostic message). Many incorrect program constructs do
 not engender undefined behavior; they are required to be diagnosed.
 Evaluation of a constant expression\iref{expr.const} never exhibits behavior explicitly
-specified as undefined in \ref{intro} through \ref{cpp}.
+specified as undefined in \ref{intro} through \ref{\lastcorechapter}.
 \end{defnote}
 
 \indexdefn{behavior!unspecified}%
@@ -722,7 +722,7 @@
 \begin{itemize}
 \item
 If a program contains no violations of the rules in
-\ref{lex} through \ref{\lastlibchapter} as well as those specified in \ref{depr},
+\ref{\firstcorechapter} through \ref{\lastlibchapter} as well as those specified in \ref{depr},
 a conforming implementation shall accept and correctly execute
 \begin{footnote}
 ``Correct execution'' can include undefined behavior
@@ -808,7 +808,7 @@
 supports all the facilities described in this document, while
 a freestanding implementation
 supports the entire \Cpp{} language
-described in \ref{lex} through \ref{cpp} and
+described in \ref{\firstcorechapter} through \ref{\lastcorechapter} and
 the subset of the library facilities described in \ref{compliance}.
 
 \pnum
@@ -958,7 +958,7 @@
 \pnum
 \indextext{standard!structure of|(}%
 \indextext{standard!structure of}%
-\ref{lex} through \ref{cpp} describe the \Cpp{} programming
+\ref{\firstcorechapter} through \ref{\lastcorechapter} describe the \Cpp{} programming
 language. That description includes detailed syntactic specifications in
 a form described in~\ref{syntax}. For convenience, \ref{gram}
 repeats all such syntactic specifications.