Add a method to indicate section address re-assignment is finished.

Prior to this patch RuntimeDyld attempted to re-apply relocations every time reassignSectionAddress was called (via MCJIT::mapSectionAddress).  In addition to being inefficient and redundant, this led to a problem when a section was temporarily moved too far away from another section with a relative relocation referencing the section being moved.  To fix this, I'm adding a new method (finalizeObject) which the client can call to indicate that it is finished rearranging section addresses so the relocations can safely be applied.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167400 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ExecutionEngine/ExecutionEngine.h

@@ -249,6 +249,13 @@ public:
                      "EE!");
   }
 
+  // finalizeObject - This method should be called after sections within an
+  // object have been relocated using mapSectionAddress.  When this method is
+  // called the MCJIT execution engine will reapply relocations for a loaded
+  // object.  This method has no effect for the legacy JIT engine or the
+  // interpeter.
+  virtual void finalizeObject() {}
+
   /// runStaticConstructorsDestructors - This method is used to execute all of
   /// the static constructors or destructors for a program.
   ///