Allow r600-llvm-compiler to be build with just radeonsi

Resync libdrm-32bit with x11 overlay
New ebuid provided by jasnn

Uses EAPI 5 along with the new python eclasses for force python2

Cheers jasnn
Resync will x11 overlay
The new ilo driver seems to be installed as i965g so try using that for dynamic switching
First attempt at converting the ebuilds to the new multilib-minimal eclass

Still slightly hacky and I'm having issues with the blockers when first switching - if someone figures out how to fix this then do let me know

Big thanks to hasufell both for the eclass and for helping me get llvm installing correctly
Add another 32bit requirement
Fixes&breakages.

Fixed a lot. Merged clang into llvm. emul-linux-x86-xlibs is now empty.
TODO: add dependencies to various [abi_x86_32]