RegexOptions.Compiled breaks .NET Core.

Summary

.NET Core 1.x appears to lack support for RegexOptions.Compiled.

Details

It just :b:reaks. Microsoft lied to me. To all of us.

Steps to reproduce

1. Use CNext in a .NET Core 1.x project.
2. Watch the thing crash because of unexpected regex options.

Notes

Should prolly bump the minimum target for compiled regex to Standard 2.0 and FX only.