[Bug libstdc++/101271] [12 Regression] error: ‘static constexpr decltype ... used before its definition

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101271

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is the workaround for the undefined llvm code, but I don't understand the
error.