[Issue 16673] New: improve cyclic module imports checker

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16673

          Issue ID: 16673
           Summary: improve cyclic module imports checker
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: critical
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: code at dawg.eu

There are quite a few projects that broke b/c we fixed the cyclic module
checker.
We should try to relax the conservative import analysis.
It seems that any static ctor/dtor only using symbols from the local module
cannot produce cycles just b/c of that and thus be marked as standalone.

Also cycles coming from imports in unittest blocks could possibly be ignored.

[¹]: https://github.com/dlang/druntime/pull/1602
[²]: https://github.com/dlang/druntime/pull/1602#issuecomment-231527759

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