class "_PEB::<unnamed>" has no field "ImageUsedLargePages"

Environment

• OS and Version: win10
• VS Code Version: 1.90.2
• C/C++ Extension Version: 1.20.5

Bug Summary and Steps to Reproduce

Bug Summary:

#include <windows.h>
typedef struct _PEB
{
  union
  {
    BOOLEAN SpareBool; // 3.51 to early 5.2

    union // late 5.2 and higher
    {
      UCHAR BitField_0x03;
      struct
      {
        // 0x01
        UCHAR ImageUsedLargePages : 1; // late 5.2 and higher
        UCHAR SpareBits_0x03_00 : 7;
      };
    };
  };
} PEB, PPEB;

int main()
{
    PEB peb{.ImageUsedLargePages = 1};
    return 0;
}

Configuration and Logs

cl -std:c++20 test.cpp can compile

{
    "configurations": [
        {
            "name": "Win32",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [
                "_DEBUG",
                "UNICODE",
                "_UNICODE"
            ],
            "windowsSdkVersion": "10.0.26100.0",
            "compilerPath": "cl.exe",
            "cStandard": "c23",
            "cppStandard": "c++23",
            "intelliSenseMode": "windows-msvc-x64"
        }
    ],
    "version": 4
}

Other Extensions

No response

Additional context

No response

Start by reproducing the diagnostic with the provided Windows C++ snippet and the listed VS Code C/C++ extension configuration. Trace how IntelliSense handles the nested anonymous unions and designated initializer, then verify that the valid code no longer reports a missing ImageUsedLargePages field while preserving the existing cl.exe behavior.