[Bug c++/124254] Accepts invalid standalone alignas declaration

[suyuchang at whu dot edu.cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124254

--- Comment #1 from Yuchang Su <suyuchang at whu dot edu.cn> ---
The following testcase may have the same issue:

char alignas(char16_t);


Clang rejects it, while accepts.