Do some small cleanup in IceTLS.h and add some markup for doxygen

src/IceTLS.h

 //===- subzero/src/IceTLS.h - thread_local workaround -----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// This file defines macros for working around the lack of support for
 /// thread_local in MacOS 10.6. It assumes std::thread is written in terms of
 /// pthread. Define ICE_THREAD_LOCAL_HACK to enable the pthread workarounds.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICETLS_H
 #define SUBZERO_SRC_ICETLS_H
 
-#if defined(_MSC_VER)
-#define ICE_ATTRIBUTE_TLS __declspec(thread)
-#else // !_MSC_VER
-#define ICE_ATTRIBUTE_TLS thread_local
-#endif // !_MSC_VER
 
-// Defines 4 macros for unifying thread_local and pthread:
-//
-// ICE_TLS_DECLARE_FIELD(Type, FieldName): Declare a static thread_local field
-// inside the current class definition. "Type" needs to be a pointer type, such
-// as int* or class Foo*.
-//
-// ICE_TLS_DEFINE_FIELD(Type, ClassName, FieldName): Define a static
-// thread_local field outside of its class definition. The field will
-// ultimately be initialized to nullptr.
-//
-// ICE_TLS_INIT_FIELD(FieldName): Ensure the thread_local field is properly
-// initialized. This is intended to be called from within a static method of
-// the field's class after main() starts (to ensure that the pthread library is
-// fully initialized) but before any uses of ICE_TLS_GET_FIELD or
-// ICE_TLS_SET_FIELD.
-//
-// ICE_TLS_GET_FIELD(Type, FieldName): Read the value of the static
-// thread_local field. Must be done within the context of its class.
-//
-// ICE_TLS_SET_FIELD(FieldName, Value): Write a value into the static
-// thread_local field. Must be done within the context of its class.
+///
+/// @defgroup /IceTLS Defines 5 macros for unifying thread_local and pthread:
+/// @{
+///
+/// \def ICE_TLS_DECLARE_FIELD(Type, FieldName)
+/// Declare a static thread_local field inside the current class definition.
+/// "Type" needs to be a pointer type, such as int* or class Foo*.
+///
+/// \def ICE_TLS_DEFINE_FIELD(Type, ClassName, FieldName)
+/// Define a static thread_local field outside of its class definition. The
+/// field will ultimately be initialized to nullptr.
+///
+/// \def ICE_TLS_INIT_FIELD(FieldName)
+/// Ensure the thread_local field is properly initialized. This is intended
+/// to be called from within a static method of the field's class after main()
+/// starts (to ensure that the pthread library is fully initialized) but before
+/// any uses of ICE_TLS_GET_FIELD or ICE_TLS_SET_FIELD.
+///
+/// \def ICE_TLS_GET_FIELD(Type, FieldName)
+/// Read the value of the static thread_local field. Must be done within the
+/// context of its class.
+///
+/// \def ICE_TLS_SET_FIELD(FieldName, Value)
+/// Write a value into the static thread_local field. Must be done within the
+/// context of its class.
 
-// TODO(stichnot): Limit this define to only the platforms that
-// absolutely require it.  And ideally, eventually remove this hack
-// altogether.
+/// \todo TODO(stichnot)
+/// Limit this define to only the platforms that absolutely require it. And
+/// ideally, eventually remove this hack altogether.
+///
+
+///
+/// \def ICE_THREAD_LOCAL_HACK
+///
 #define ICE_THREAD_LOCAL_HACK
 #ifdef ICE_THREAD_LOCAL_HACK
 
 // For a static thread_local field F of a class C, instead of declaring and
 // defining C::F, we create two static fields:
 //   static pthread_key_t F__key;
 //   static int F__initStatus;
 //
 // The F__initStatus field is used to hold the result of the
 // pthread_key_create() call, where a zero value indicates success, and a
@@ skipping 18 matching lines @@
   }
 #define ICE_TLS_GET_FIELD(FieldName)                                           \
   (assert(FieldName##__initStatus == 0),                                       \
    static_cast<FieldName##__type>(pthread_getspecific(FieldName##__key)))
 #define ICE_TLS_SET_FIELD(FieldName, Value)                                    \
   (assert(FieldName##__initStatus == 0),                                       \
    pthread_setspecific(FieldName##__key, (Value)))
 
 #else // !ICE_THREAD_LOCAL_HACK
 
+#if defined(_MSC_VER)
+#define ICE_ATTRIBUTE_TLS __declspec(thread)
+#else // !_MSC_VER
+#define ICE_ATTRIBUTE_TLS thread_local
+#endif // !_MSC_VER
+
+
 #define ICE_TLS_DECLARE_FIELD(Type, FieldName)                                 \
   static ICE_ATTRIBUTE_TLS Type FieldName
 #define ICE_TLS_DEFINE_FIELD(Type, ClassName, FieldName)                       \
   ICE_ATTRIBUTE_TLS Type ClassName::FieldName = nullptr
 #define ICE_TLS_INIT_FIELD(FieldName)
 #define ICE_TLS_GET_FIELD(FieldName) (FieldName)
 #define ICE_TLS_SET_FIELD(FieldName, Value) (FieldName = (Value))
 
 #endif // !ICE_THREAD_LOCAL_HACK
 
+///
+/// @}
+///
+
 #endif // SUBZERO_SRC_ICETLS_H