[Bug c++/123329] [13/14/15/16 regression] ICE: unexpected expression 'T' of kind template_parm_index

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123329

--- Comment #1 from Sam James <sjames at gcc dot gnu.org> ---
In 15, it gets worse as we stop emitting the first error, and just ICE (before,
we'd error-then-ICE).