Add and use System.Linux.time_t for time_t

Add and use System.Linux.time_t for time_t

	PR ada/54040
	* s-linux-x32.ads: New file.
	* s-osprim-x32.adb: Likewise.
	* s-linux.ads (time_t): New type.
	* s-linux-alpha.ads (time_t):  Likewise.
	* s-linux-hppa.ads (time_t):  Likewise.
	* s-linux-mipsel.ads (time_t):  Likewise.
	* s-linux-sparc.ads (time_t):  Likewise.
	* s-osinte-linux.ads (time_t): Mark it private.  Replace long
	with System.Linux.time_t.
	(timespec): Replace long with time_t.
	* s-osinte-posix.adb (To_Timespec): Likewise.
	* s-taprop-linux.adb (timeval): Replace C.long with
	System.OS_Interface.time_t.
	* gcc-interface/Makefile.in (LIBGNAT_TARGET_PAIRS): Replace
	s-linux.ads with s-linux-x32.ads, s-osprim-posix.adb with
	s-osprim-x32.adb for x32.

From-SVN: r204840