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/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index 530ab46..0bb0fa3 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -55,7 +55,7 @@
     bool isIdempotentRMW(AtomicRMWInst *AI);
     bool simplifyIdempotentRMW(AtomicRMWInst *AI);
   };
-}
+} // namespace
 
 char AtomicExpand::ID = 0;
 char &llvm::AtomicExpandID = AtomicExpand::ID;