Installation of CityHash by Craig Silverstein

llvm-svn: 146329
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 53d2fb0aa26bc73c89bae3c74afd103f28602c65
diff --git a/include/string b/include/string
index 4457e4a..620e6f8 100644
--- a/include/string
+++ b/include/string
@@ -3916,7 +3916,7 @@
 size_t _LIBCPP_INLINE_VISIBILITY __do_string_hash(_Ptr __p, _Ptr __e)
 {
     typedef typename iterator_traits<_Ptr>::value_type value_type;
-    return __murmur2<size_t>()(__p, (__e-__p)*sizeof(value_type));
+    return __murmur2_or_cityhash<size_t>()(__p, (__e-__p)*sizeof(value_type));
 }
 
 template<class _CharT, class _Traits, class _Allocator>