The now-active mailing list thread can be found here. Dylan McKay has been working on an AVR back-end for LLVM over the past few months and he's hoping to now mainline the code.
This back-end is for targeting the Atmel AVR 8-bit RISC micro-controller that's been around since the late 90s. AVR devices have found their way into a wide range of applications across multiple industries. The popular Arduino micro-controller is one such device based on the megaAVR family.
The current AVR-LLVM back-end is capable of generating Assembly files and ELF object files for the architecture. Those wishing to see the current out-of-tree work on the AVR LLVM back-end can find it on GitHub. Prior to being accepted into mainline LLVM, all of the code must go through a review process, after which it will initially be marked as an "experimental" back-end inside LLVM.