https://issues.dlang.org/show_bug.cgi?id=24172

          Issue ID: 24172
           Summary: Error when compiling with std_regex_* debug conditions
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: trivial
          Priority: P1
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: info@lapyst.by

While trying to debug some compile time regexes (ctRegex), I used the debug conditions `std_regex_*`, and it produces some trivial errors:

- they enable usage of `writeln` while not importing `std.stdio` in all places
- `BacktrackingMatcher.ctAtomCode` is not generating a valid case when debug
statements are present (needs explicit falltrough for IR.End)
- parseRegex has a typo; uses `fixupStack.data` instead of `g.fixupStack.data`

I work on a WIP patch for that all, which I will link here from my fork of phobos once I got the issue number for it.

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