fix(windows): extract mdk-sdk via realpath to avoid CMake symlink rejection

[abdelaziz-mahdy]

Fixes #366.

Problem

flutter build windows --release fails in fvp_setup_deps while extracting mdk-sdk-windows-x64.7z:

CMake Error: Problem with archive_write_header(): Cannot extract through symlink
  ...\windows\flutter\ephemeral\.plugin_symlinks\fvp
Failed to extract mdk-sdk.

On Flutter Windows, CMAKE_CURRENT_SOURCE_DIR is reached through the generated plugin symlink (.plugin_symlinks/fvp). Newer CMake's cmake -E tar extracts with ARCHIVE_EXTRACT_SECURE_SYMLINKS and refuses to write entries through a symlinked directory. The download itself is fine (verified: byte-identical 7z, valid magic) — only the extraction step is rejected. This started when CI runner images bumped their bundled CMake (≥ 3.31), with no project change.

Fix

Resolve CMAKE_CURRENT_SOURCE_DIR to its real (non-symlinked) path and extract there:

get_filename_component(MDK_SDK_EXTRACT_DIR "${CMAKE_CURRENT_SOURCE_DIR}" REALPATH)
execute_process(
  COMMAND ${CMAKE_COMMAND} -E tar "xvf" ${MDK_SDK_SAVE}
  WORKING_DIRECTORY ${MDK_SDK_EXTRACT_DIR}
  ...)

get_filename_component(... REALPATH) is used instead of file(REAL_PATH) to stay compatible with the plugin's cmake_minimum_required(VERSION 3.17). On platforms where the path is not a symlink, REALPATH is a no-op (resolves to the same directory), so behavior is unchanged elsewhere. The subsequent include(${CMAKE_CURRENT_SOURCE_DIR}/mdk-sdk/.../FindMDK.cmake) still resolves through the symlink (reading through a symlink is fine).

Verification

Built the example/ app on windows-latest (same runner image that fails today, same plugin-symlink scenario, same mdk-sdk download). It now extracts and builds successfully:

Downloading mdk-sdk from https://sourceforge.net/projects/mdk-sdk/files/nightly/mdk-sdk-windows-x64.7z
MDK_SDK_MD5_SAVE: 1e59ba0aed23f2723642c69fec07888e
Building Windows application...                    79.3s
√ Built build\windows\x64\runner\Release\fvp_example.exe

(no Cannot extract through symlink.)

[gemini-code-assist]

Code Review

This pull request resolves the real path of CMAKE_CURRENT_SOURCE_DIR to prevent extraction failures on Flutter Windows, where the directory is accessed via a symlink and newer CMake versions refuse to extract through symlinks. The feedback recommends wrapping the path variables in double quotes within the execute_process command to avoid build failures when paths contain spaces.

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[gemini-code-assist]

To prevent potential build failures when the project path or the build directory contains spaces (which is common on Windows, e.g., under C:\Program Files or user directories with spaces), it is highly recommended to wrap ${MDK_SDK_SAVE} and ${MDK_SDK_EXTRACT_DIR} in double quotes within the execute_process command.

    execute_process(
      COMMAND ${CMAKE_COMMAND} -E tar "xvf" "${MDK_SDK_SAVE}" # "--format=7zip"
      WORKING_DIRECTORY "${MDK_SDK_EXTRACT_DIR}"
      OUTPUT_STRIP_TRAILING_WHITESPACE
      RESULT_VARIABLE EXTRACT_RET
    )