https://issues.dlang.org/show_bug.cgi?id=15987

          Issue ID: 15987
           Summary: core.sys.windows.msacm remains pseudo definitions
           Product: D
           Version: D2
          Hardware: All
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody@puremagic.com
          Reporter: jiki@red.email.ne.jp

I found this when verifying the struct sizes for Win32-x64. Some of the buffer sizes are pseudo values, as its comment says.

I'll send a PR.

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