I don't see a reason to add the `copyWithNewScope()` API over to
`MDLocation` -- it seems to be a holdover from when creating locations
required knowing details of operand layout -- so change
`AddDiscriminators` to call `MDLocation::get()` directly. Should be no
functionality change here.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234824 91177308-0d34-0410-b5e6-96231b3b80d8