[Bug c++/81717] [c++ concepts] - simple "define function if not defined" code doesn't compile, no errors generated

[jordok at wp dot pl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81717

--- Comment #1 from Przemysław Czechowski <jordok at wp dot pl> ---
Created attachment 41926
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41926&action=edit
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