[MCJIT] Clean up RuntimeDyld's quirky object-ownership/modification scheme.

Previously, when loading an object file, RuntimeDyld (1) took ownership of the
ObjectFile instance (and associated MemoryBuffer), (2) potentially modified the
object in-place, and (3) returned an ObjectImage that managed ownership of the
now-modified object and provided some convenience methods. This scheme accreted
over several years as features were tacked on to RuntimeDyld, and was both
unintuitive and unsafe (See e.g. http://llvm.org/PR20722).

This patch fixes the issue by removing all ownership and in-place modification
of object files from RuntimeDyld. Existing behavior, including debugger
registration, is preserved.

Noteworthy changes include:

(1) ObjectFile instances are now passed to RuntimeDyld by const-ref.
(2) The ObjectImage and ObjectBuffer classes have been removed entirely, they
    existed to model ownership within RuntimeDyld, and so are no longer needed.
(3) RuntimeDyld::loadObject now returns an instance of a new class,
    RuntimeDyld::LoadedObjectInfo, which can be used to construct a modified
    object suitable for registration with the debugger, following the existing
    debugger registration scheme.
(4) The JITRegistrar class has been removed, and the GDBRegistrar class has been
    re-written as a JITEventListener.

This should fix http://llvm.org/PR20722 .



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222810 91177308-0d34-0410-b5e6-96231b3b80d8

tools/lli/RemoteMemoryManager.cpp

@@ -14,7 +14,6 @@
 
 #include "RemoteMemoryManager.h"
 #include "llvm/ExecutionEngine/ExecutionEngine.h"
-#include "llvm/ExecutionEngine/ObjectImage.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Format.h"
 
@@ -78,7 +77,7 @@ sys::MemoryBlock RemoteMemoryManager::allocateSection(uintptr_t Size) {
 }
 
 void RemoteMemoryManager::notifyObjectLoaded(ExecutionEngine *EE,
-                                                const ObjectImage *Obj) {
+                                             const object::ObjectFile &Obj) {
   // The client should have called setRemoteTarget() before triggering any
   // code generation.
   assert(Target);