More zic cleanup.

The workaround the IANA guys chose to get rid of the clang warning
we'd silenced in commit 23ed2ba8 turns out not to satisfy Coverity.
Go back to the previous solution, ie, remove the useless comparison
to SIZE_MAX.  (In principle, there could be machines out there where
it's not useless because ptrdiff_t is wider than size_t.  But the whole
thing is pretty academic anyway, as we could never approach this limit
for any sane estimate of the amount of data that zic will ever be asked
to work with.)

Also, s/lineno/lineno_t/g, because if we accept their decision to start
using "lineno" as a typedef, it is going to have very unpleasant
consequences in our next pgindent run.  Noted that while fooling with
pltcl yesterday.

src/timezone/zic.c

@@ -48,13 +48,13 @@ static ptrdiff_t const PTRDIFF_MAX = MAXVAL(ptrdiff_t, TYPE_BIT(ptrdiff_t));
 #endif
 
 /* The type and printf format for line numbers.  */
-typedef int lineno;
+typedef int lineno_t;
 #define PRIdLINENO "d"
 
 struct rule
 {
 	const char *r_filename;
-	lineno		r_linenum;
+	lineno_t	r_linenum;
 	const char *r_name;
 
 	zic_t		r_loyear;		/* for example, 1986 */
@@ -91,7 +91,7 @@ struct rule
 struct zone
 {
 	const char *z_filename;
-	lineno		z_linenum;
+	lineno_t	z_linenum;
 
 	const char *z_name;
 	zic_t		z_gmtoff;
@@ -169,7 +169,7 @@ static int	leapcnt;
 static bool leapseen;
 static zic_t leapminyear;
 static zic_t leapmaxyear;
-static lineno linenum;
+static lineno_t linenum;
 static int	max_abbrvar_len = PERCENT_Z_LEN_BOUND;
 static int	max_format_len;
 static zic_t max_year;
@@ -178,7 +178,7 @@ static bool noise;
 static bool print_abbrevs;
 static zic_t print_cutoff;
 static const char *rfilename;
-static lineno rlinenum;
+static lineno_t rlinenum;
 static const char *progname;
 static ptrdiff_t timecnt;
 static ptrdiff_t timecnt_alloc;
@@ -276,7 +276,7 @@ static ptrdiff_t nzones_alloc;
 struct link
 {
 	const char *l_filename;
-	lineno		l_linenum;
+	lineno_t	l_linenum;
 	const char *l_from;
 	const char *l_to;
 };
@@ -430,14 +430,13 @@ ecpyalloc(char const * str)
 }
 
 static void *
-growalloc(void *ptr, size_t itemsize, ptrdiff_t nitems, ptrdiff_t * nitems_alloc)
+growalloc(void *ptr, size_t itemsize, ptrdiff_t nitems, ptrdiff_t *nitems_alloc)
 {
 	if (nitems < *nitems_alloc)
 		return ptr;
 	else
 	{
-		ptrdiff_t	nitems_max = PTRDIFF_MAX - WORK_AROUND_QTBUG_53071;
-		ptrdiff_t	amax = nitems_max < SIZE_MAX ? nitems_max : SIZE_MAX;
+		ptrdiff_t	amax = PTRDIFF_MAX - WORK_AROUND_QTBUG_53071;
 
 		if ((amax - 1) / 3 * 2 < *nitems_alloc)
 			memory_exhausted(_("integer overflow"));
@@ -451,7 +450,7 @@ growalloc(void *ptr, size_t itemsize, ptrdiff_t nitems, ptrdiff_t * nitems_alloc
  */
 
 static void
-eats(char const * name, lineno num, char const * rname, lineno rnum)
+eats(char const * name, lineno_t num, char const * rname, lineno_t rnum)
 {
 	filename = name;
 	linenum = num;
@@ -460,7 +459,7 @@ eats(char const * name, lineno num, char const * rname, lineno rnum)
 }
 
 static void
-eat(char const * name, lineno num)
+eat(char const * name, lineno_t num)
 {
 	eats(name, num, NULL, -1);
 }
@@ -1157,7 +1156,7 @@ infile(const char *name)
 	const struct lookup *lp;
 	int			nfields;
 	bool		wantcont;
-	lineno		num;
+	lineno_t	num;
 	char		buf[BUFSIZ];
 
 	if (strcmp(name, "-") == 0)