[ORC] Pass symbol name to discard by const reference.

This saves some unnecessary atomic ref-counting operations.

llvm-svn: 343927
diff --git a/llvm/unittests/ExecutionEngine/Orc/OrcTestCommon.h b/llvm/unittests/ExecutionEngine/Orc/OrcTestCommon.h
index ae6dce6..284a1e3 100644
--- a/llvm/unittests/ExecutionEngine/Orc/OrcTestCommon.h
+++ b/llvm/unittests/ExecutionEngine/Orc/OrcTestCommon.h
@@ -112,7 +112,8 @@
     Materialize(std::move(R));
   }
 
-  void discard(const orc::JITDylib &JD, orc::SymbolStringPtr Name) override {
+  void discard(const orc::JITDylib &JD,
+               const orc::SymbolStringPtr &Name) override {
     if (Discard)
       Discard(JD, std::move(Name));
     else