reverting constexpr bool

It is only initialized with a constexpr, later updated at runtime

Signed-off-by: Dan Hoeflinger <dan.hoeflinger@intel.com>

include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl.h

@@ -844,7 +844,7 @@ struct __gen_set_mask
 
         auto __res = oneapi::dpl::__internal::__pstl_lower_bound(__set_b, std::size_t{0}, __nb, __val_a, __comp);
 
-        constexpr bool bres =
+        bool bres =
             _IsOpDifference::value; //initialization is true in case of difference operation; false - intersection.
         if (__res == __nb || __comp(__val_a, __set_b[__res]))
         {