[Issue 21134] New: time_t should probably be defined as a 64-bit type on x86-64

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21134

          Issue ID: 21134
           Summary: time_t should probably be defined as a 64-bit type on
                    x86-64
           Product: D
           Version: D2
          Hardware: All
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: andrej.mitrovich at gmail.com

https://github.com/dlang/druntime/blob/349d63750d55d078426d4f433cba512625f8a3a3/src/core/sys/windows/stdc/time.d#L42

This definition seems to have remained unchanged since at least 2008 and
probably older:
https://github.com/dlang/druntime/blob/6837c0cd426f7e828aec1a2bdc941ac9b722dd14/import/stdc/time.d#L49

This is around the time x64 Windows originally started getting released.

But nowadays MSDN says that `time_t` defaults to being a 64-bit type:

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/time-time32-time64?view=vs-2019

> time is a wrapper for _time64 and **time_t is, by default, equivalent to __time64_t**.

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