XCore target: Fix llvm.eh.return and EH info register handling
XCore target: addMemOperand as necessary

BuildMI instructions were not including MachineMemOperand information.
This was discovered by 'SingleSource/Benchmarks/Stanford/Oscar' failing
due to a FrameIndex load incorrectly being hoisted by postra-machine-licm.
No other tests have been found to fail.
XCore target: Handle common linkage