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/atomic_load_add.ll b/llvm/test/CodeGen/AMDGPU/atomic_load_add.ll
index 20c6854..4b014e0 100644
--- a/llvm/test/CodeGen/AMDGPU/atomic_load_add.ll
+++ b/llvm/test/CodeGen/AMDGPU/atomic_load_add.ll
@@ -1,5 +1,5 @@
-; RUN: llc -march=amdgcn -mcpu=SI -verify-machineinstrs < %s | FileCheck %s -check-prefix=SI -check-prefix=FUNC
-; RUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck %s -check-prefix=SI -check-prefix=FUNC
+; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck %s -check-prefix=SI -check-prefix=FUNC
+; RUN: llc -march=amdgcn -mcpu=tonga -mattr=-flat-for-global -verify-machineinstrs < %s | FileCheck %s -check-prefix=SI -check-prefix=FUNC
 ; RUN: llc -march=r600 -mcpu=redwood < %s | FileCheck -check-prefix=R600 -check-prefix=FUNC %s
 
 ; FUNC-LABEL: {{^}}atomic_add_local: