Support was added to Clang today for supporting -march=bdver4, which exposes the instruction set extensions supported by the upcoming CPU/APUs based upon AMD's Excavator. Excavator/bdver4 is the successor to their Steamroller micro-architecture. Excavator cores expected to appear in 2015 within Carrizo APUs. Excavator adds support for the AVX2 and RDRAND instruction set extensions of Steamroller bdver3.
On the GCC side, AMD Excavator landed in GCC 4.9. With today's Git commit for bdver4 targeting in Clang, it will be part of the LLVM 3.5 release this summer -- well ahead of seeing any AMD Excavator processors.