[libc++][NFC] Refactor __enable_ifs in <cstddef> to be defaulted

template arguments

This makes the library more consistent and reduces the size of mangled
names a bit as a bonus.

Author: philnik777

libcxx/include/cstddef

@@ -112,32 +112,30 @@ _LIBCPP_HIDE_FROM_ABI constexpr byte  operator~ (byte __b) noexcept
     ));
 }
 
-template <class _Tp>
-using _EnableByteOverload = __enable_if_t<is_integral<_Tp>::value, byte>;
-
-template <class _Integer>
-_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer> &
-  operator<<=(byte& __lhs, _Integer __shift) noexcept
-  { return __lhs = __lhs << __shift; }
-
-template <class _Integer>
-_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer>
-  operator<< (byte  __lhs, _Integer __shift) noexcept
-  { return static_cast<byte>(static_cast<unsigned char>(static_cast<unsigned int>(__lhs) << __shift)); }
-
-template <class _Integer>
-_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer> &
-  operator>>=(byte& __lhs, _Integer __shift) noexcept
-  { return __lhs = __lhs >> __shift; }
-
-template <class _Integer>
-_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer>
-  operator>> (byte  __lhs, _Integer __shift) noexcept
-  { return static_cast<byte>(static_cast<unsigned char>(static_cast<unsigned int>(__lhs) >> __shift)); }
-
-template <class _Integer, class = _EnableByteOverload<_Integer> >
-_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Integer
-  to_integer(byte __b) noexcept { return static_cast<_Integer>(__b); }
+template <class _Integer, __enable_if_t<is_integral<_Integer>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI constexpr byte& operator<<=(byte& __lhs, _Integer __shift) noexcept {
+  return __lhs = __lhs << __shift;
+}
+
+template <class _Integer, __enable_if_t<is_integral<_Integer>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI constexpr byte operator<<(byte __lhs, _Integer __shift) noexcept {
+  return static_cast<byte>(static_cast<unsigned char>(static_cast<unsigned int>(__lhs) << __shift));
+}
+
+template <class _Integer, __enable_if_t<is_integral<_Integer>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI constexpr byte& operator>>=(byte& __lhs, _Integer __shift) noexcept {
+  return __lhs = __lhs >> __shift;
+}
+
+template <class _Integer, __enable_if_t<is_integral<_Integer>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI constexpr byte operator>>(byte __lhs, _Integer __shift) noexcept {
+  return static_cast<byte>(static_cast<unsigned char>(static_cast<unsigned int>(__lhs) >> __shift));
+}
+
+template <class _Integer, __enable_if_t<is_integral<_Integer>::value, int> = 0>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Integer to_integer(byte __b) noexcept {
+  return static_cast<_Integer>(__b);
+}
 
 } // namespace std