@aeva In principle, I ran Gentoo on an Intel Core 2 Duo Mac Mini until that computer broke, so for a Core 2 Duo, you don't even need a second modern computer for compiling (though that would be faster), you can just install and use Gentoo.
I can confirm that Gentoo works on BIOS systems no problem, I've personally installed it on multiple systems that only have BIOS.
It has Clang 20 and libsdl3.
Although, if you don't actually want Gentoo, you just want your stuff to work: did you test yet whether the latest Debian boots from that USB stick? I remember installing it successfully on BIOS-only hardware a few years ago, but the latest version (Debian 13, which is the only one that has SDL3).
Unfortunately can't test it for you because they dropped 32-bit x86 support in that latest version
)