Fix usage of C++14 constexpr in HasZeroOrOneBit
diff --git a/src/include/nxt/EnumClassBitmasks.h b/src/include/nxt/EnumClassBitmasks.h
index 63804a4..a17c505 100644
--- a/src/include/nxt/EnumClassBitmasks.h
+++ b/src/include/nxt/EnumClassBitmasks.h
@@ -77,8 +77,7 @@
     template<typename T>
     constexpr bool HasZeroOrOneBits(T value) {
         using Integral = typename UnderlyingType<T>::type;
-        Integral v = static_cast<Integral>(value);
-        return (v & (v - 1)) == 0;
+        return (static_cast<Integral>(value) & (static_cast<Integral>(value) - 1)) == 0;
     }
 
     template<typename T1, typename T2, typename = typename std::enable_if<