[ARM64][CollectLOH] Add some comments to explain how the LOHs
framework works (for the compiler part), since the design
document is not available.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205379 91177308-0d34-0410-b5e6-96231b3b80d8
DebugInfo: Introduce DebugLocList to encapsulate a list of DebugLocEntries and an MC Label to refer to them

This removes the magic-number-esque code creating/retrieving the same
label for a debug_loc entry from two places and removes the last small
piece of reusable logic from emitDebugLoc so that there will be less
duplication when refactoring it into two functions (one for debug_loc,
the other for debug_loc.dwo).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205382 91177308-0d34-0410-b5e6-96231b3b80d8
Split debug_loc and debug_loc.dwo emission into two separate functions

Based on code review feedback from Eric Christopher on r204697

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205385 91177308-0d34-0410-b5e6-96231b3b80d8