Avoid int to string conversion in Twine or raw_ostream contexts.

Some output changes from uppercase hex to lowercase hex, no other functionality change intended.

llvm-svn: 321526
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 60f96d0..f268801 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -419,8 +419,8 @@
     CmdArgs.push_back("-plugin-opt=thinlto");
 
   if (unsigned Parallelism = getLTOParallelism(Args, D))
-    CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=jobs=") +
-                                         llvm::to_string(Parallelism)));
+    CmdArgs.push_back(
+        Args.MakeArgString("-plugin-opt=jobs=" + Twine(Parallelism)));
 
   // If an explicit debugger tuning argument appeared, pass it along.
   if (Arg *A = Args.getLastArg(options::OPT_gTune_Group,