[llvm] Separate out reverse iteration flag into its own header

[mgrang]

Summary

This will ease out adding reverse iteration flags to other containers by simply including the header.

[dblaikie]

Seems good to me

llvm/trunk/include/llvm/ADT/SmallPtrSet.h

 // This file defines the SmallPtrSet class.  See the doxygen comment for
 // SmallPtrSetImplBase for more details on the algorithm used.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_SMALLPTRSET_H
 #define LLVM_ADT_SMALLPTRSET_H
 
-#include "llvm/Config/abi-breaking.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
+#include "llvm/Support/ReverseIteration.h"
 #include "llvm/Support/type_traits.h"
 #include <cassert>
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
 #include <initializer_list>
 #include <iterator>
 #include <utility>
 
 namespace llvm {
 
-#if LLVM_ENABLE_ABI_BREAKING_CHECKS
-template <class T = void> struct ReverseIterate { static bool value; };
-#if LLVM_ENABLE_REVERSE_ITERATION
-template <class T> bool ReverseIterate<T>::value = true;
-#else
-template <class T> bool ReverseIterate<T>::value = false;
-#endif
-#endif
-
 /// SmallPtrSetImplBase - This is the common code shared among all the
 /// SmallPtrSet<>'s, which is almost everything.  SmallPtrSet has two modes, one
 /// for small and one for large sets.
 ///
 /// Small sets use an array of pointers allocated in the SmallPtrSet object,
 /// which is treated as a simple array of pointers.  When a pointer is added to
 /// the set, the array is scanned to see if the element already exists, if not
 /// the element is 'pushed back' onto the array.  If we run out of space in the

llvm/trunk/include/llvm/Support/ReverseIteration.h

+#ifndef LLVM_SUPPORT_REVERSEITERATION_H
+#define LLVM_SUPPORT_REVERSEITERATION_H
+
+#include "llvm/Config/abi-breaking.h"
+
+namespace llvm {
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+template <class T = void> struct ReverseIterate { static bool value; };
+#if LLVM_ENABLE_REVERSE_ITERATION
+template <class T> bool ReverseIterate<T>::value = true;
+#else
+template <class T> bool ReverseIterate<T>::value = false;
+#endif
+#endif
+}
+
+#endif