Implement LLVM JIT side of GDB JIT debugging interface

lib/CodeGen/ELFWriter.h

Index: lib/CodeGen/ELFWriter.h
===================================================================
--- lib/CodeGen/ELFWriter.h	(revision 82403)
+++ lib/CodeGen/ELFWriter.h	(working copy)
@@ -28,6 +28,7 @@
   class ELFSection;
   struct ELFSym;
   class GlobalVariable;
+  class JITDebugRegisterer;
   class Mangler;
   class MachineCodeEmitter;
   class MachineConstantPoolEntry;
@@ -51,6 +52,7 @@
   ///
   class ELFWriter : public MachineFunctionPass {
     friend class ELFCodeEmitter;
+    friend class JITDebugRegisterer;
   public:
     static char ID;