C++11: Make 'enum struct', enum-base and opaque enum decls work.

For declarations like:
enum struct Foo : long int;

Change-Id: Id813efdbc31c8d70a4b40bb0101dc33a8dd2556a
Reviewed-by: hjk <qthjk@ovi.com>

tests/auto/cplusplus/cxx11/data/enums.1.cpp

@@ -0,0 +1,11 @@
+enum { A, B };
+enum : int;
+enum : int { A, B };
+enum Foo1 { A, B };
+enum Foo2 : int;
+enum Foo3 : int { A, B };
+enum class Foo4 : int;
+enum struct Foo5;
+enum class Foo6 { A, B };
+enum struct Foo7 { A, B };
+enum struct Foo8 : long long;