[Patch, libstdc++/65420] Use constexpr variables as regex_constans flags

[Jonathan Wakely]

On 15 March 2015 at 08:09, Tim Shen wrote:
> Did a little bit refectoring on regex_constants, so that users won't
> be polluted too much (they are not enum types anymore).

I think this is overengineered and unnecessary.

All it needs is something like:

enum syntax_option_type : unsigned { };
constexpr syntax_option_type icase = ...;