AMDGPU: Fix assert when erroring on a call

[arsenm]

Summary

For some reason an assert is now hit when a valid chain is not returned, so return the entry chain.

[arsenm]

Fix another assert. Test erroring multiple times in the same module

[• tstellarAMD]

LGTM.

[arsenm]

r269948

lib/Target/AMDGPU/AMDGPUISelLowering.cpp

SDValue AMDGPUTargetLowering::LowerCall(CallLoweringInfo &CLI,
   if (const ExternalSymbolSDNode *G = dyn_cast<ExternalSymbolSDNode>(Callee))
     FuncName = G->getSymbol();
   else if (const GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee))
     FuncName = G->getGlobal()->getName();
 
   DiagnosticInfoUnsupported NoCalls(
       Fn, "unsupported call to function " + FuncName, CLI.DL.getDebugLoc());
   DAG.getContext()->diagnose(NoCalls);
-  return SDValue();
+  return DAG.getEntryNode();
 }
 
 SDValue AMDGPUTargetLowering::LowerDYNAMIC_STACKALLOC(SDValue Op,
                                                       SelectionDAG &DAG) const {
   const Function &Fn = *DAG.getMachineFunction().getFunction();
 
   DiagnosticInfoUnsupported NoDynamicAlloca(Fn, "unsupported dynamic alloca",
                                             SDLoc(Op).getDebugLoc());