message: Improve impl of get_environmental_variable()
diff: @@ -75,7 +75,6 @@ namespace vcpkg::System
  optional<std::wstring> get_environmental_variable(const wchar_t* varname) noexcept
  {
  - std::wstring ret;
  wchar_t* buffer;
  _wdupenv_s(&buffer, nullptr, varname);
  @@ -83,10 +82,8 @@ namespace vcpkg::System
  {
  return nullptr;
  }
  -
  - ret = buffer;
  - free(buffer);
  - return std::make_unique<std::wstring>(ret);
  + std::unique_ptr<wchar_t, void(__cdecl *)(void*)> bufptr(buffer, free);
  + return std::make_unique<std::wstring>(buffer);
  }
  void set_environmental_variable(const wchar_t* varname, const wchar_t* varvalue) noexcept
  