Parse some type of `auto` declaration as `EponymousTemplateDeclaration`

[ghost]

templated enums decl are called EponymousTemplateDeclaration, but not auto. Maybe they should be the same.

enum ep1(T) = T.sizeof; // EponymousTemplateDeclaration
auto ep2(T) = T.sizeof;  // for now VariableDeclaration...

(https://github.com/dlang-community/libdparse/blob/master/src/dparse/parser.d#L2015)