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/sign_extend.ll b/llvm/test/CodeGen/AMDGPU/sign_extend.ll
index 0593817..875351c 100644
--- a/llvm/test/CodeGen/AMDGPU/sign_extend.ll
+++ b/llvm/test/CodeGen/AMDGPU/sign_extend.ll
@@ -1,5 +1,5 @@
 ; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefixes=GCN,SI %s
-; RUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck -check-prefixes=GCN,VI %s
+; RUN: llc -march=amdgcn -mcpu=tonga -mattr=-flat-for-global -verify-machineinstrs < %s | FileCheck -check-prefixes=GCN,VI %s
 
 ; GCN-LABEL: {{^}}s_sext_i1_to_i32:
 ; GCN: v_cndmask_b32_e64