[XCore] Use static relocation model by default.

This allows us to get get rid of a hack in XCoreTargetObjectFile where the
the DataRel* sections were overridden.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181116 91177308-0d34-0410-b5e6-96231b3b80d8