Remove std::move on return when it could prevent copy elision.

Found by -Wpessimizing-move, no functional change. The APFloat and
PassManager change doesn't affect codegen as returning a by-value
argument will always result in a move.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236316 91177308-0d34-0410-b5e6-96231b3b80d8

utils/yaml-bench/YAMLBench.cpp

@@ -69,7 +69,7 @@ static std::string prettyTag(yaml::Node *N) {
   if (StringRef(Tag).startswith("tag:yaml.org,2002:")) {
     std::string Ret = "!!";
     Ret += StringRef(Tag).substr(18);
-    return std::move(Ret);
+    return Ret;
   }
   std::string Ret = "!<";
   Ret += Tag;