gallium/radeon: always add +DumpCode to the LLVM target machine for LLVM <= 3.5

gallium/radeon: always add +DumpCode to the LLVM target machine for LLVM <= 3.5

It's the same behavior that we use for later LLVM.

Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>