Fix constexpr failure on C++11-based buildbots.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@322507 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/algorithms/alg.nonmodifying/alg.find.end/find_end_pred.pass.cpp

@@ -25,7 +25,7 @@ struct count_equal
 {
     static unsigned count;
     template <class T>
-    TEST_CONSTEXPR bool operator()(const T& x, const T& y)
+    TEST_CONSTEXPR_CXX14 bool operator()(const T& x, const T& y)
         {++count; return x == y;}
 };