[docs] Fix doxygen comments wrongly attached to the clang namespace

Looking at the Doxygen-generated documentation for the clang namespace
currently shows several random comments from different parts of the
codebase. These are caused by:

- File doc comments that aren't marked with \file, so they're attached to
  the next declaration, which is usually "namespace clang {".
- Class doc comments placed before the namespace rather than before the
  class.

This commit fixes these comments. The generated doxygen documentation now
has proper docs for several classes and files, and the docs for the clang
namespace is now empty.

Differential Revision: https://reviews.llvm.org/D96738

clang/include/clang/AST/ExternalASTSource.h

@@ -462,10 +462,10 @@ public:
 
 } // namespace clang
 
-/// Specialize PointerLikeTypeTraits to allow LazyGenerationalUpdatePtr to be
-/// placed into a PointerUnion.
 namespace llvm {
 
+/// Specialize PointerLikeTypeTraits to allow LazyGenerationalUpdatePtr to be
+/// placed into a PointerUnion.
 template<typename Owner, typename T,
          void (clang::ExternalASTSource::*Update)(Owner)>
 struct PointerLikeTypeTraits<

clang/include/clang/Analysis/FlowSensitive/DataflowValues.h

@@ -19,13 +19,14 @@
 #include "clang/Analysis/ProgramPoint.h"
 #include "llvm/ADT/DenseMap.h"
 
+namespace clang {
+
 //===----------------------------------------------------------------------===//
 /// Dataflow Directional Tag Classes.  These are used for tag dispatching
 ///  within the dataflow solver/transfer functions to determine what direction
 ///  a dataflow analysis flows.
 //===----------------------------------------------------------------------===//
 
-namespace clang {
 namespace dataflow {
   struct forward_analysis_tag {};
   struct backward_analysis_tag {};

clang/include/clang/StaticAnalyzer/Core/PathSensitive/LoopUnrolling.h

@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-///
+/// \file
 /// This header contains the declarations of functions which are used to decide
 /// which loops should be completely unrolled and mark their corresponding
 /// CFGBlocks. It is done by tracking a stack of loops in the ProgramState. This
@@ -18,7 +18,6 @@
 ///   has to be initialized by a literal in the corresponding initStmt.
 /// - Does not contain goto, switch and returnStmt.
 ///
-///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_STATICANALYZER_CORE_PATHSENSITIVE_LOOPUNROLLING_H

clang/include/clang/StaticAnalyzer/Core/PathSensitive/LoopWidening.h

@@ -5,7 +5,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-///
+/// \file
 /// This header contains the declarations of functions which are used to widen
 /// loops which do not otherwise exit. The widening is done by invalidating
 /// anything which might be modified by the body of the loop.