Change time_t to 64-bit by default

In order to avoid the year 2038 problem, define time_t to a signed
integer with at least 64-bits.  The type for time_t can be forced to
long with the --enable-newlib-long-time_t configure option or with the
_USE_LONG_TIME_T system configuration define.

Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>

newlib/libc/include/sys/_types.h

@@ -186,7 +186,11 @@ typedef void *_iconv_t;
 
 typedef	_CLOCK_T_	__clock_t;
 
-#define	_TIME_T_	long		/* time() */
+#if defined(_USE_LONG_TIME_T) || __LONG_MAX__ > 0x7fffffffL
+#define	_TIME_T_ long
+#else
+#define	_TIME_T_ __int_least64_t
+#endif
 typedef	_TIME_T_	__time_t;
 
 #define	_CLOCKID_T_ 	unsigned long

newlib/libc/include/sys/config.h

@@ -283,6 +283,12 @@
 #endif
 #endif
 
+#ifdef _WANT_USE_LONG_TIME_T
+#ifndef _USE_LONG_TIME_T
+#define _USE_LONG_TIME_T
+#endif
+#endif
+
 /* If _MB_EXTENDED_CHARSETS_ALL is set, we want all of the extended
    charsets.  The extended charsets add a few functions and a couple
    of tables of a few K each. */