enum.h tries to automatically detect whether it is running with C++11 support.
If not, it emits alternative code that is supposed to work on compilers
supporting C++98 and variadic macros. This code is largely interface-compatible
with the C++11 code, with the following semantic differences:
- No compile-time stringization. This is done upon first use of a function other
than to_integral.
- Implicit conversion to integral types. This is due to the lack of enum class
support.
- The values _name, _names, _values are replaced with functions _name_, _names_,
_values_.
