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

The patch is generated using this command:

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

To reduce churn, not touching namespaces spanning less than 10 lines.

llvm-svn: 240270
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index d9dc4df..db3f196 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -140,7 +140,7 @@
       PlaceholderKind = (BuiltinType::Kind) 0;
     }
   };
-}
+} // namespace
 
 // The Try functions attempt a specific way of casting. If they succeed, they
 // return TC_Success. If their way of casting is not appropriate for the given