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/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 2969bad..141990b 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -179,7 +179,7 @@
   /// in-loop predecessors of this chain.
   unsigned LoopPredecessors;
 };
-}
+} // namespace
 
 namespace {
 class MachineBlockPlacement : public MachineFunctionPass {
@@ -267,7 +267,7 @@
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 };
-}
+} // namespace
 
 char MachineBlockPlacement::ID = 0;
 char &llvm::MachineBlockPlacementID = MachineBlockPlacement::ID;
@@ -1185,7 +1185,7 @@
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 };
-}
+} // namespace
 
 char MachineBlockPlacementStats::ID = 0;
 char &llvm::MachineBlockPlacementStatsID = MachineBlockPlacementStats::ID;