[Bug c++/104113] invalid template argument causes the type to become int which confuses the rest of the diagnostic

["nickhuang99 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104113

--- Comment #6 from qingzhe huang <nickhuang99 at hotmail dot com> ---
How about this simple fix? (see the patch above.) 
Instead of return "error_mark_node" by condition of
"!cp_parser_simulate_error", we now report error immediately. The rational of
this fix is that "cp_parser_simulate_error" is only making sense when we
already see error, i.e. "CP_PARSER_STATUS_KIND_ERROR". Otherwise, we should
just report error.
I did a full build and check, it seems fine with me. For example, 

104091.cpp: In function ‘void g()’:
104091.cpp:8:7: error: ‘auto’ not permitted in template argument
    8 |     A<auto> x = A<short>();
      |       ^~~~
104091.cpp:8:13: error: variable ‘A<auto> x’ has initializer but incomplete
type
    8 |     A<auto> x = A<short>();
      |             ^


Also I noticed previous testcase (i.e. g++.dg/DRs/dr625.C) is too relaxed with
error message by allowing inaccurate "invalid template argument" or "cannot
convert ..." instead of "auto not permitted".

If this makes sense to you, I am happy to provide more testcases and correct
those old testcases.