[Issue 20717] Unsilenced bogus "undefined identifier" error from speculative collision

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20717

--- Comment #2 from Basile-z <b2.temp at gmx.com> ---
Created attachment 1779
  --> https://issues.dlang.org/attachment.cgi?id=1779&action=edit
workaround

As officially I dont participate to dlang anymore but also as a commit of mine
causes the regression I send a patch.

The fix is not really good but comes with explanations about what was done in
first place, i.e for issue 15795. Ideally issue 15795 should be fixed in
another way but I remember that I could not find a better way when I made the
PR.

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