headers: crt: disable getpid in UWP builds

It is not allowed.

It was already disabled in process.h from 7c2e0a371f0f631513611988688f0a6b19ea9731

https://docs.microsoft.com/en-us/cpp/cppcx/crt-functions-not-supported-in-universal-windows-platform-apps

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