I'm seeing some warnings coming up in GCC 13.2 (default Ubuntu). We're running 11.4 in CI, which isn't much order (2 months) in terms of release dates. @pmienk do we have an upper bound on GCC support presently?
So it's not complaining about the FLAGS as unknown, and reports them, and also libsecp is outputting the CFLAGS. If you do it prior to install it sets the process environment, but I think the way we are passing args it also would work.