AMDGPU: skip AMDGPUAttributor pass on R600 some more. (#162418)

This is a follow-up for #162207, where I neglected to skip the second
use of AMDGPUAttributor for R600 targets. This use is covered by the
test lld/test/ELF/lto/r600.ll.

Author: jyknight

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -966,7 +966,7 @@ void AMDGPUTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB) {
             PM.addPass(InternalizePass(mustPreserveGV));
             PM.addPass(GlobalDCEPass());
           }
-          if (EnableAMDGPUAttributor) {
+          if (EnableAMDGPUAttributor && getTargetTriple().isAMDGCN()) {
             AMDGPUAttributorOptions Opt;
             if (HasClosedWorldAssumption)
               Opt.IsClosedWorld = true;