[NFC][DFAJT] Place cl::opts in the llvm namespace (llvm#162212)

Along the lines of [llvm#161240](vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html "Open Issue or Pull Request llvm#161240 on GitHub")

Author: mtrofin

llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp

@@ -89,6 +89,7 @@ STATISTIC(NumTransforms, "Number of transformations done");
 STATISTIC(NumCloned, "Number of blocks cloned");
 STATISTIC(NumPaths, "Number of individual paths threaded");
 
+namespace llvm {
 static cl::opt<bool>
     ClViewCfgBefore("dfa-jump-view-cfg-before",
                     cl::desc("View the CFG before DFA Jump Threading"),
@@ -119,6 +120,7 @@ static cl::opt<unsigned>
     CostThreshold("dfa-cost-threshold",
                   cl::desc("Maximum cost accepted for the transformation"),
                   cl::Hidden, cl::init(50));
+} // namespace llvm
 
 static cl::opt<double> MaxClonedRate(
     "dfa-max-cloned-rate",