https://issues.dlang.org/show_bug.cgi?id=19432

          Issue ID: 19432
           Summary: Cannot initialize ulong with decimal value above
                    signed long range
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: johanengelen@weka.io

Initialization of an ulong with a decimal within range, but outside long range,
gives a "Error: signed integer overflow" compiler error.
Testcase:
```
enum a = 18446744073709551615; // 2^^64 - 1
ulong b = 18446744073709551615; // 2^^64 - 1
```

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