Simplify error_code class

Remove "not an error" detection trait. Use fixed CellNotAnError class.
Use constructor overload to disable reporting it.

rpcs3/Emu/Cell/ErrorCodes.h

@@ -14,32 +14,12 @@ class error_code
 	// Implementation must be provided independently
 	static s32 error_report(const fmt_type_info* sup, u64 arg, const fmt_type_info* sup2, u64 arg2);
 
-	// Helper type
-	enum class not_an_error : s32
-	{
-		__not_an_error // SFINAE marker
-	};
-
-	// __not_an_error tester
-	template<typename ET, typename = void>
-	struct is_error : std::integral_constant<bool, std::is_enum<ET>::value || std::is_integral<ET>::value>
-	{
-	};
-
-	template<typename ET>
-	struct is_error<ET, std::enable_if_t<sizeof(ET::__not_an_error) != 0>> : std::false_type
-	{
-	};
-
 	// Common constructor
 	template<typename ET>
 	error_code(const ET& value)
 		: value(static_cast<s32>(value))
 	{
-		if constexpr(is_error<ET>::value)
-		{
-			this->value = error_report(fmt::get_type_info<fmt_unveil_t<ET>>(), fmt_unveil<ET>::get(value), nullptr, 0);
-		}
+		this->value = error_report(fmt::get_type_info<fmt_unveil_t<ET>>(), fmt_unveil<ET>::get(value), nullptr, 0);
 	}
 
 	// Error constructor (2 args)
@@ -55,11 +35,24 @@ class error_code
 	}
 };
 
+enum CellNotAnError : s32
+{
+	CELL_OK     = 0,
+	CELL_CANCEL = 1,
+};
+
+// Constructor specialization that doesn't trigger reporting
+template <>
+constexpr FORCE_INLINE error_code::error_code<CellNotAnError>(const CellNotAnError& value)
+	: value(value)
+{
+}
+
 // Helper function for error_code
 template <typename T>
-constexpr FORCE_INLINE error_code::not_an_error not_an_error(const T& value)
+constexpr FORCE_INLINE CellNotAnError not_an_error(const T& value)
 {
-	return static_cast<error_code::not_an_error>(static_cast<s32>(value));
+	return static_cast<CellNotAnError>(static_cast<s32>(value));
 }
 
 template <typename T, typename>
@@ -79,15 +72,6 @@ struct ppu_gpr_cast_impl<error_code, void>
 	}
 };
 
-
-enum CellNotAnError : s32
-{
-	CELL_OK     = 0,
-	CELL_CANCEL = 1,
-
-	__not_an_error
-};
-
 enum CellError : u32
 {
 	CELL_EAGAIN        = 0x80010001, // The resource is temporarily unavailable