[Bug c++/122550] [14/15/16 Regression] constrained hidden template friend alongside existing declaration is ambiguous

[egas.g.ribeiro at tecnico dot ulisboa.pt]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122550

--- Comment #7 from Egas  Ribeiro <egas.g.ribeiro at tecnico dot ulisboa.pt> ---
v2 with Patrick's suggestion:
https://gcc.gnu.org/pipermail/gcc-patches/2025-December/704242.html