On Sat, 19 Mar 2022 at 17:53, David Edelsohn wrote:
> The %{} syntax is the "Specs language" used for options processing by
> GCC. It is not related to autoconf. The options processing is
> handled in gcc.c. Please see the comment in gcc/gcc.cc beginning with
> "The Specs Language".
And https://gcc.gnu.org/onlinedocs/gcc/Spec-Files.html