https://issues.dlang.org/show_bug.cgi?id=21980

          Issue ID: 21980
           Summary: importC: _Thread_local allowed as storage class for
                    return type
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: ibuclaw@gdcproject.org

This is illegal as per C99 6.7.1-4:
_Thread_local shall not appear in the declaration specifiers of a function
declaration.

---
_Thread_local int invalid();

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