WinStoreCompat: Add a getpid replacement using GetCurrentProcessId

git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64/trunk@5698 4407c894-4637-0410-b4f5-ada5f102cad1
Added _set_purecall_handler fallback implementation.


git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64/trunk@5705 4407c894-4637-0410-b4f5-ada5f102cad1
Use GPLv3 or later license

git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64/trunk@5706 4407c894-4637-0410-b4f5-ada5f102cad1