Merge 2018-11 CWG Motion 8

P1002R1 Try-catch blocks in constexpr functions

Fixes #2400

Author: zygoloid

source/declarations.tex

@@ -797,22 +797,20 @@
 each of its parameter types shall be a literal type;
 
 \item
-its \grammarterm{function-body} shall be
-\tcode{= delete}, \tcode{= default}, or
-a \grammarterm{compound-statement}
-that does not contain
-
+its \grammarterm{function-body} shall not contain
 \begin{itemize}
 \item an \grammarterm{asm-definition},
 \item a \tcode{goto} statement,
 \item an identifier label\iref{stmt.label},
-\item a \grammarterm{try-block}, or
 \item a definition of a variable
 of non-literal type or
 of static or thread storage duration or
 for which no initialization is performed.
 \end{itemize}
-
+\begin{note}
+A \grammarterm{function-body} that is \tcode{= delete} or \tcode{= default}
+contains none of the above.
+\end{note}
 \end{itemize}
 
 \begin{example}
@@ -853,10 +851,7 @@
 the class shall not have any virtual base classes;
 
 \item
-each of the parameter types shall be a literal type;
-
-\item
-its \grammarterm{function-body} shall not be a \grammarterm{function-try-block}.
+each of the parameter types shall be a literal type.
 \end{itemize}
 
 In addition, either its \grammarterm{function-body} shall be