Enable FeatureFlatForGlobal on Volcanic Islands

This switches to the workaround that HSA defaults to
for the mesa path.

This should be applied to the 4.0 branch.

Patch by Vedran Miletić <vedran@miletic.net>

llvm-svn: 292982
diff --git a/llvm/test/CodeGen/AMDGPU/madmk.ll b/llvm/test/CodeGen/AMDGPU/madmk.ll
index 7185085..27fbf58 100644
--- a/llvm/test/CodeGen/AMDGPU/madmk.ll
+++ b/llvm/test/CodeGen/AMDGPU/madmk.ll
@@ -1,5 +1,5 @@
 ; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefix=GCN -check-prefix=SI %s
-; XUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck -check-prefix=GCN -check-prefix=VI %s
+; XUN: llc -march=amdgcn -mcpu=tonga -mattr=-flat-for-global -verify-machineinstrs < %s | FileCheck -check-prefix=GCN -check-prefix=VI %s
 
  ; FIXME: None of these trigger madmk emission anymore. It is still
  ; possible, but requires the correct registers to be used which is