[ORC] Errorize the ORC APIs.

This patch updates the ORC layers and utilities to return and propagate
llvm::Errors where appropriate. This is necessary to allow ORC to safely handle
error cases in cross-process and remote JITing.

llvm-svn: 307350
diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h
index 5268bc5..95b04fd 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h
@@ -417,7 +417,7 @@
                        StubMap &Stubs) = 0;
 
   /// \brief Resolve relocations to external symbols.
-  void resolveExternalSymbols();
+  Error resolveExternalSymbols();
 
   // \brief Compute an upper bound of the memory that is required to load all
   // sections