CWG3079 Allow empty-declarations in anonymous unions

Author: eisenwave

source/classes.tex

@@ -3357,7 +3357,8 @@
 \indextext{access control!anonymous \tcode{union}}%
 \indextext{restriction!anonymous \tcode{union}}%
 Each \grammarterm{member-declaration} in the \grammarterm{member-specification}
-of an anonymous union shall either define one or more public non-static data members or
+of an anonymous union shall define one or more public non-static data members,
+be an \grammarterm{empty-declaration}, or
 be a \grammarterm{static_assert-declaration}.
 Nested types, anonymous unions, and functions
 shall not be declared within an anonymous union.