headers: crt: disable process APIs in winstore builds

It's not allowed to launch another process (as far as 2016 doc goes):
https://docs.microsoft.com/en-us/cpp/cppcx/crt-functions-not-supported-in-universal-windows-platform-apps?view=vs-2019

"The functionality is not available in UWP apps. A UWP app cannot invoke
another UWP app or a desktop app."

Signed-off-by: Liu Hao <lh_mouse@126.com>