[Bug c++/104091] -std=c++20 causing meaningless error message "'auto' not allowed in alias declaration" which should be "missing template arguments after ..."

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104091

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
A slight variation from PR 101221:

template<class T> struct S;
template<class T> using SS = S;


For comparison, Clang and EDG give exactly the same diagnostic for all examples
above irrespective of C++14/17/20 mode.