Cygwin: implement extensible clock interface

- Drop hires_[nm]s clocks, rename hires.h to clock.h.

- Implement clk_t class as an extensible clock class in new file clock.cc.

- Introduce get_clock(clock_id) returning a pointer to the clk_t instance
  for clock_id.  Provide the following methods along the lines of the former
  hires classes:

	void		clk_t::nsecs (struct timespec *);
	ULONGLONG	clk_t::nsecs ();
	LONGLONG	clk_t::usecs ();
	LONGLONG	clk_t::msecs ();
	void 		clk_t::resolution (struct timespec *);

- Add CLOCK_REALTIME_COARSE, CLOCK_MONOTONIC_RAW, CLOCK_MONOTONIC_COARSE
  and CLOCK_BOOTTIME clocks.

- Allow clock_nanosleep, pthread_condattr_setclock and timer_create to use
  all new clocks (both clocks should be usable with a small tweak, though).

- Bump DLL major version to 2.12.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/ntdll.h

@@ -793,7 +793,8 @@ typedef struct _KUSER_SHARED_DATA
   KSYSTEM_TIME InterruptTime;
   BYTE Reserved2[0x2c8];
   ULONG DismountCount;
-  /* A lot more follows... */
+  BYTE Reserved3[0xd0];
+  UINT64 InterruptTimeBias;
 } KUSER_SHARED_DATA, *PKUSER_SHARED_DATA;
 
 /* Checked on 64 bit. */