Support atimers and CPU profiler via profile.c on MS-Windows.

Support atimers and CPU profiler via profile.c on MS-Windows.

 src/w32proc.c (sig_mask, crit_sig): New static variables.
 (sys_signal): Support SIGALRM and SIGPROF.
 (sigemptyset, sigaddset, sigfillset, sigprocmask)
 (pthread_sigmask, setpgrp): Moved here from w32.c.  sigaddset,
 sigfillset, and sigprocmask are no longer no-ops.
 (sigismember): New function.
 (struct itimer_data): New definition.
 (ticks_now, real_itimer, prof_itimer, clocks_min, crit_real)
 (crit_prof): New static variables.
 (MAX_SINGLE_SLEEP): New definition.
 (timer_loop, stop_timer_thread, term_timers, init_timers)
 (start_timer_thread, getitimer, setitimer): New functions.
 (alarm): No longer a no-op, calls setitimer.
 src/w32.c (term_ntproc): Call term_timers.
 (init_ntproc): Make sure all signals are unblocked at startup, to
 erase any traces of dumping.  Call init_timers.
 src/w32fns.c (hourglass_timer, HOURGLASS_ID): Remove.
 Windows-specific code to display the hourglass mouse pointer is no
 longer used.
 (w32_wnd_proc): Remove code that handled the WM_TIMER message due
 to hourglass timer expiration.
 (start_hourglass, cancel_hourglass, DEFAULT_HOURGLASS_DELAY):
 Remove, no longer used.
 (w32_note_current_window, show_hourglass, hide_hourglass): New
 functions, in support of hourglass cursor display similar to other
 window systems.
 (syms_of_w32fns): Don't initialize hourglass_timer.
 src/xdisp.c (start_hourglass, cancel_hourglass): Now used on
 WINDOWSNT as well.
 (start_hourglass) [WINDOWSNT]: Call w32_note_current_window.
 src/w32.h (init_timers, term_timers): Add prototypes.

 nt/inc/sys/time.h (ITIMER_REAL, ITIMER_PROF): Define.
 (struct itimerval): Define.
 (getitimer, setitimer): Add prototypes.
 nt/inc/ms-w32.h <sigset_t> [_MSVC_VER]: Make the typedef consistent
 with MinGW.
 (SA_RESTART, SIGPROF): Define.
 nt/config.nt (HAVE_SETITIMER): Define to 1.