DateDiff() function does not support DateTime64:
```
SELECT dateDiff('second', toDateTime64('1927-01-01 00:00:00', 0, 'UTC'), toDateTime64('1927-01-01 00:00:00', 0, 'UTC'))

0 rows in set. Elapsed: 0.024 sec. 

Received exception from server (version 21.5.1):
Code: 44. DB::Exception: Received from localhost:9000. DB::Exception: Illegal column for first argument of function dateDiff, must be Date or DateTime: While processing dateDiff('second', toDateTime64('1927-01-01 00:00:00', 0, 'UTC'), toDateTime64('1927-01-01 00:00:00', 0, 'UTC')). 
```
#include <DataTypes/DataTypeDateTime.h>
#include <DataTypes/DataTypeDateTime64.h>
#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnString.h>
#include <Columns/ColumnsNumber.h>
#include <Functions/IFunctionImpl.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/FunctionFactory.h>