Fixed/added namespace ending comments using clang-tidy. NFC

The patch is generated using this command:

tools/clang/tools/extra/clang-tidy/tool/run-clang-tidy.py -fix \
  -checks=-*,llvm-namespace-comment -header-filter='llvm/.*|clang/.*' \
  llvm/lib/


Thanks to Eugene Kosov for the original patch!

llvm-svn: 240137
diff --git a/llvm/lib/Transforms/Utils/FlattenCFG.cpp b/llvm/lib/Transforms/Utils/FlattenCFG.cpp
index 4eb3e3d..40a48c0 100644
--- a/llvm/lib/Transforms/Utils/FlattenCFG.cpp
+++ b/llvm/lib/Transforms/Utils/FlattenCFG.cpp
@@ -46,7 +46,7 @@
   FlattenCFGOpt(AliasAnalysis *AA) : AA(AA) {}
   bool run(BasicBlock *BB);
 };
-}
+} // namespace
 
 /// If \param [in] BB has more than one predecessor that is a conditional
 /// branch, attempt to use parallel and/or for the branch condition. \returns