Fixes broken tests introduced in 2203a8564c5faba383a3512f8244dba12d79da16
Looks like on Windows 7, if a dll has no entry point, no tls callbacks are run. On Windows 10, the `DLL_PROCESS_ATTACH` is run but nothing else.
By having an entry point, everything is run like you'd expect
Also changes the tests to test the full set of process/thread attach/detach
-- v4: kernel32/tests: Fix tls callback tests on Windows 7