You know what? I actually changed my mind thinking about this lately, and now agree the best way to go is probably just use whatever upstream does. The goal is to use upstream as if it was a library, and actually target making it one that we could simply use.
Yeah, this is my thinking too and using GNU regex would simplify things. I can try to prepare a patch to get it working on linux - I don't think it will be that hard (unless I run into some unpredictable issues). For windows I guess it means adding
https://github.com/universal-ctags/ctags/tree/master/gnu_regex
compiling it and using it for regex parsing, right? I'll leave that to someone with better knowledge of building for windows and autotools.