DwarfCompileUnit: Remove unnecessary OwningPtr<T>::get() call

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194901 91177308-0d34-0410-b5e6-96231b3b80d8
DwarfCompileUnit: Push type safety of DIDescriptor through CompileUnit::createAndAddDIE.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194902 91177308-0d34-0410-b5e6-96231b3b80d8