Rename '-enable-arc-opts=false' to '-disable-arc-opts'.

Part of the migration to the new driver. With this commit, the only
failures in the test suite using the new frontend are features we don't
intend to port over. Hooray!

Swift SVN r13198

lib/Frontend/CompilerInvocation.cpp

@@ -571,6 +571,8 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
       llvm_unreachable("Unknown SIL linking option!");
   }
 
+  Opts.EnableARCOptimizations = !Args.hasArg(OPT_disable_arc_opts);
+
   return false;
 }