[ORC] Add an Error return to the JITCompileCallbackManager::grow method.

Calling grow may result in an error if, for example, this is a callback
manager for a remote target. We need to be able to return this error to the
callee.

llvm-svn: 312429
diff --git a/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp b/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp
index 844746f..24258ec 100644
--- a/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp
+++ b/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp
@@ -21,7 +21,7 @@
   DummyCallbackManager() : JITCompileCallbackManager(0) {}
 
 public:
-  void grow() override { llvm_unreachable("not implemented"); }
+  Error grow() override { llvm_unreachable("not implemented"); }
 };
 
 class DummyStubsManager : public orc::IndirectStubsManager {