gcc-15/16 compiling the std module and the --with-default-libstdcxx-abi compiler flag

Hi,

I tried to compile the std module using the latest gcc sources, by using :

g++ -std=c++23 -fmodules -fsearch-include-path -c bits/std.cc

and it worked OK. I've tried to compile some simple programs with it, and
it worked as expected.

However, when I build the compiler with the option

--with-default-libstdcxx-abi = gcc4-compatible

The std module failed with various compiler errors. I guess this is
something to be expected, but I would like to ask if it is also something
that may be "fixed" in the future or not.

Thank you very much.