[except.throw] Add comma (#7118)

Author: Andreas-Krug

source/exceptions.tex

@@ -264,7 +264,7 @@
 an incomplete type\iref{basic.types.general},
 an abstract class type\iref{class.abstract},
 or a pointer to an incomplete type other than
-\cv{}~\keyword{void}\iref{basic.compound}
+\cv{}~\keyword{void}\iref{basic.compound},
 the program is ill-formed.
 
 \pnum