[Bug c++/89833] [9 Regression] sorry, unimplemented: string literal in function template signature

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89833

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
N.B. I think this is only a regression against recent trunk. It's a new C++2a
feature which isn't supported in any released version.