gcc-15 backport for Debian 13 Trixie

Hello!

I'm curious how do DDs/DMs do backporting of fresh GCC toolchains on
stable releases.

Notes: I'm currently working on merge requests for mingw-w64, and
gcc-mingw-w64 was recently rebased on top of gcc 15, so I'd need to
get gcc 15 working on Debian 13 Trixie to continue local research and
tests. I've tried once to backport GCC 15 on my own but the resulting
dependencies are somewhat broken (e.g. libcc1 for gcc itself).
Backporting binutils was a quite simple task but not gcc.

PS: I can perform tests on Debian Sid, but for some reasons I need to
do this on Trixie too.

-- 
SY,
Konstantin Demin