[Ada] Use OS_Time for interface to TZ functions.

gcc/ada/

	* libgnat/a-calend.adb: Remove time_t, replace with OS_Time.
	* libgnat/s-os_lib.ads: Fix comments regarding time_t conversion
	functions to reflect the use of To_Ada in in Ada.Calendar
	package body.
	* sysdep.c (__gnat_localtime_tzoff): Use OS_Time instead of
	time_t.
3 files changed