Port 'make check_time_t_alternatives' to Solaris 10.

* Makefile (check_time_t_alternatives): Don't assume 'diff'
has the -q option, since POSIX does not require -q.
* NEWS: Document this.
Port 'bool' usage to Sun C 5.12.

* zic.c (inzcont, inzone, is_alpha, yearistype):
Fix prototype to match function, as the C standard requires.
* NEWS: Mention the use of 'bool'.
Port C macro defaults to Solaris and Irix.

This is mostly for convenience, so that plain 'make' works out of
the box on Solaris, instead of having to run something awkward like
'make CFLAGS="-xc99=all -DHAVE_INCOMPATIBLE_CTIME_R=1"', and
similarly for Irix 6.5.
* private.h (_POSIX_PTHREAD_SEMANTICS):
* private.h, zdump.c (__EXTENSIONS__):
New macros, to make Solaris headers more like what we want out
of the box.
(LLONG_MAX, LLONG_MIN): Default from __LONG_LONG_MAX__ if it's defined.
This simplifies later code.
(SCNdFAST64, PRIdMAX): Don't assume they're defined when
INT_FAST64_MAX is, as that's not true on Solaris 10 + Sun C 5.12.
(PRIuMAX): Likewise, for Solaris 11 + Sun C 5.12.
* zdump.c (HAVE_LOCALTIME_RZ): Default to 1 only if TM_ZONE.
* Makefile, NEWS: Document this.