[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This change is incorrect, r11-532-g4b38d56dbac6742b038551a36ec80200313123a1 is
wrong to reject that assignment operator. The declarator-id is "operator=" and
so doesn't contain a template-id at all.