Add line tracking support to FormattedStream 
- previously formatted_raw_ostream tracked columns, now it tracks lines too
- used by (upcoming) DebugIR pass to know the line number to connect to each IR
  instruction



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181463 91177308-0d34-0410-b5e6-96231b3b80d8
Pull up AssemblyWriter interface into header to allow subclassing
- made all functions virtual so that subclasses can specialize them
- add printInstructionLine so that subclasses can choose whether or not to
  print the newline character (without having to implement printBasicBlock()
- added a second constructor to AssemblyWriter that does not require a
  SlotTracker, as required in order to keep the SlotTracker helper class outside
  AsmWriter.h and buried in the implementation.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181466 91177308-0d34-0410-b5e6-96231b3b80d8
Add DebugIR pass -- emits IR file and replace source lines with IR lines in MD
- requires existing debug information to be present
- fixes up file name and line number information in metadata
- emits a "<orig_filename>-debug.ll" succinct IR file (without !dbg metadata
  or debug intrinsics) that can be read by a debugger
- initialize pass in opt tool to enable the "-debug-ir" flag
- lit tests to follow



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181467 91177308-0d34-0410-b5e6-96231b3b80d8