This is for building code in the "app" mode (for Windows
Store apps/RT/metro/modern UI/appcontainer), which restricts API
usage and uses the Windows Runtime APIs for threading instead of the
old Win32 functions that aren't available for such apps.
This is similar to building for Windows Phone, but without the phone
specific libraries.
The common parts are abstracted to a common include makefile, that
both the targets "msvc-app" and "msvc-wp" use.
