crt: tests: compile t_winmain with `make check` without running it

Test t_winmain creates a window which makes it unsuitable for automated
environments such as GitHub CI. However, we can compile it as part of
`make check` without actually running it.

Once compiled, this program can be run locally as `./testcases/t_winmain.exe`.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>