says the following:
Seastar supports GCC and Clang. Ports to other compilers are
welcome.
The last two major releases of a compiler are supported (e.g.
GCC 13 and GCC 14). Patches to support older versions are welcome,
as long as they don't require onerous compromises.
This document is probably out of date - the last two major versions of GCC
are 14 and 15 - not 13 and 14. But in any case, GCC 11.4 is older than that,
and not officially supported on modern versions of Seastar.
That being said, if you can write a patch that fixes whatever doesn't compile
on GCC 11.4, while not hurting the code in any significant way, you are very
welcome to propose such a patch. But in my opinion the better approach is
to upgrade to a more modern compiler.