amd: remove support for LLVM 3.9

Only these are supported:
- LLVM 4.0
- LLVM 5.0
- LLVM 6.0
- master (7.0)

Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
12 files changed