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/flat-address-space.ll b/llvm/test/CodeGen/AMDGPU/flat-address-space.ll
index 0cfe688..55b5482 100644
--- a/llvm/test/CodeGen/AMDGPU/flat-address-space.ll
+++ b/llvm/test/CodeGen/AMDGPU/flat-address-space.ll
@@ -1,6 +1,6 @@
 ; RUN: llc -O0 -mtriple=amdgcn-mesa-mesa3d -mcpu=bonaire < %s | FileCheck  %s
-; RUN: llc -O0 -mtriple=amdgcn-mesa-mesa3d -mcpu=tonga < %s | FileCheck  %s
-; RUN: llc -O0 -mtriple=amdgcn-amd-amdhsa -mcpu=fiji < %s | FileCheck -check-prefixes=CHECK,HSA %s
+; RUN: llc -O0 -mtriple=amdgcn-mesa-mesa3d -mcpu=tonga -mattr=-flat-for-global < %s | FileCheck  %s
+; RUN: llc -O0 -mtriple=amdgcn-amd-amdhsa -mcpu=fiji -mattr=-flat-for-global < %s | FileCheck -check-prefixes=CHECK,HSA %s
 
 ; Disable optimizations in case there are optimizations added that
 ; specialize away generic pointer accesses.