Pass DebugLoc and SDLoc by const ref.

This used to be free, copying and moving DebugLocs became expensive
after the metadata rewrite. Passing by reference eliminates a ton of
track/untrack operations. No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272512 91177308-0d34-0410-b5e6-96231b3b80d8
155 files changed