php_win32_signal_system_ctrl_handler() is called from a kernel thread,
so the former initialization of `vm_interrupt_flag` has no effect,
since it is defined as thread-local. This is, however, not necessary,
since the CTRL signal handling is supposed to work only for the main
thread anyway. We therefore change `vm_interrupt_flag` and the related
variables to true globals.
This also allows us to unmark the respective test case as XFAIL.
Furthermore, `vm_interrupt_flag` is declared as `zend_bool *`, so we
better treat it such.
