Add generic support for hashing StringRef objects using the new hashing library.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152003 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/StringRef.h

@@ -19,6 +19,7 @@ namespace llvm {
   template<typename T>
   class SmallVectorImpl;
   class APInt;
+  class hash_code;
 
   /// StringRef - Represent a constant reference to a string, i.e. a character
   /// array and a length, which need not be null terminated.
@@ -490,6 +491,9 @@ namespace llvm {
 
   /// @}
 
+  /// \brief Compute a hash_code for a StringRef.
+  hash_code hash_value(StringRef S);
+
   // StringRefs can be treated like a POD type.
   template <typename T> struct isPodLike;
   template <> struct isPodLike<StringRef> { static const bool value = true; };