[ORC] Create a new SymbolStringPool by default in ExecutionSession constructor.

This makes the common case of constructing an ExecutionSession tidier.

llvm-svn: 329013
diff --git a/llvm/unittests/ExecutionEngine/Orc/ObjectTransformLayerTest.cpp b/llvm/unittests/ExecutionEngine/Orc/ObjectTransformLayerTest.cpp
index eacd3e0..6ad3c19 100644
--- a/llvm/unittests/ExecutionEngine/Orc/ObjectTransformLayerTest.cpp
+++ b/llvm/unittests/ExecutionEngine/Orc/ObjectTransformLayerTest.cpp
@@ -179,8 +179,7 @@
 TEST(ObjectTransformLayerTest, Main) {
   MockBaseLayer M;
 
-  SymbolStringPool SSP;
-  ExecutionSession ES(SSP);
+  ExecutionSession ES(std::make_shared<SymbolStringPool>());
 
   // Create one object transform layer using a transform (as a functor)
   // that allocates new objects, and deals in unique pointers.