[Bug c++/52761] [C++11] Missing diagnostic for opaque unscoped enum declaration without base

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52761

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
clang declared this as a GNU extention :)
<source>:2:6: error: redeclaration of already-defined enum 'E' is a GNU
extension [-Werror,-Wgnu-redeclared-enum]
enum E;  // illegal
     ^
<source>:1:6: note: previous definition is here
enum E { X };
     ^