Disable use list order on the gold plugin.

It turns out that his is *really* slow. With this change the link of
clang with plugin-opt=emit-llvm goes from 41 to 26 seconds.

We can add an option to enable it again if needed.

llvm-svn: 256302

llvm/tools/gold/gold-plugin.cpp

@@ -756,7 +756,7 @@ static void saveBCFile(StringRef Path, Module &M) {
   raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
   if (EC)
     message(LDPL_FATAL, "Failed to write the output file.");
-  WriteBitcodeToFile(&M, OS, /* ShouldPreserveUseListOrder */ true);
+  WriteBitcodeToFile(&M, OS, /* ShouldPreserveUseListOrder */ false);
 }
 
 static void codegen(std::unique_ptr<Module> M) {