Bug 1625138 - Part 10: Replace mozilla::IsEnum with std::is_enum. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D68364

--HG--
extra : moz-landing-system : lando

mfbt/Atomics.h

@@ -24,6 +24,7 @@
 #include <atomic>
 
 #include <stdint.h>
+#include <type_traits>
 
 namespace mozilla {
 
@@ -447,7 +448,7 @@ class Atomic<T*, Order> : public detail::AtomicBaseIncDec<T*, Order> {
  * The atomic store and load operations and the atomic swap method is provided.
  */
 template <typename T, MemoryOrdering Order>
-class Atomic<T, Order, typename EnableIf<IsEnum<T>::value>::Type>
+class Atomic<T, Order, typename EnableIf<std::is_enum_v<T>>::Type>
     : public detail::AtomicBase<T, Order> {
   typedef typename detail::AtomicBase<T, Order> Base;
 

mfbt/TypeTraits.h

@@ -235,24 +235,6 @@ struct IsPointerHelper<T*> : TrueType {};
 template <typename T>
 struct IsPointer : detail::IsPointerHelper<typename RemoveCV<T>::Type> {};
 
-namespace detail {
-
-// __is_enum is a supported extension across all of our supported compilers.
-template <typename T>
-struct IsEnumHelper : IntegralConstant<bool, __is_enum(T)> {};
-
-}  // namespace detail
-
-/**
- * IsEnum determines whether a type is an enum type.
- *
- * mozilla::IsEnum<enum S>::value is true;
- * mozilla::IsEnum<enum S*>::value is false;
- * mozilla::IsEnum<int>::value is false;
- */
-template <typename T>
-struct IsEnum : detail::IsEnumHelper<typename RemoveCV<T>::Type> {};
-
 /* 20.9.4.3 Type properties [meta.unary.prop] */
 
 /**