message: Use System::set_environmental_variable()
diff: @@ -38,8 +38,8 @@ namespace vcpkg::Commands::Build
  }
  // If these environment variables are set while running the VS2017 developer prompt, it will not correctly initialize the build environment.
  - _wputenv_s(L"VSINSTALLDIR", L"");
  - _wputenv_s(L"DevEnvDir", L"");
  + System::set_environmental_variable(L"VSINSTALLDIR", L"");
  + System::set_environmental_variable(L"DevEnvDir", L"");
  const fs::path ports_cmake_script_path = paths.ports_cmake;
  const Environment::vcvarsall_and_platform_toolset vcvarsall_bat = Environment::get_vcvarsall_bat(paths);
  