[ORC] Fix a memory leak in LLVMOrcIRTransformLayerSetTransform.

This function heap-allocates a ThreadSafeModule (the current C bindings assume
that TSMs are always heap-allocated), but was failing to free it.

Should fix http://llvm.org/PR56953.

llvm/lib/ExecutionEngine/Orc/OrcV2CBindings.cpp

@@ -892,7 +892,10 @@ void LLVMOrcIRTransformLayerSetTransform(
               assert(!TSMRef && "TSMRef was not reset to null on error");
               return unwrap(Err);
             }
-            return std::move(*unwrap(TSMRef));
+            assert(TSMRef && "Transform succeeded, but TSMRef was set to null");
+            ThreadSafeModule Result = std::move(*unwrap(TSMRef));
+            LLVMOrcDisposeThreadSafeModule(TSMRef);
+            return std::move(Result);
           });
 }