Now it actually compiles and works fine.

After enabling abi_x86_32 on only 62 packages.

Now emul-linux-x86-{xlibs,opengl} are empty, clang binary is 64-bit, libclc compiles fine, mesa compiles fine, even with wayland and vdpau support, and I think almost all dependencies are specified. All left is to add dependencies to the fake emul-linux-x86-xlibs on packages[abi_x86_32].

The changes are actually huge. As clang was merged into llvm (to avoid compiling llvm twice), it will be needed to unmerge clang first because of file collisions. I'm almost sure there's a way to move file ownership using /profiles/updates but I don't know how. I will update the pull request if I do.