crt: tests: add new test t_wassert

This test is similar to t_assert, except it tests CRT function `_wassert`.

Unlike `_assert`, CRT function `_wassert` properly behaves in case when
`stderr` was set to Unicode translation mode.

When this test is compiled with msvcrt.dll, or msvcr80.dll and later, it also
sets `stderr` to Unicode transaltion mode before triggering an `assert`.

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