Fix strflocaltime on DST values

The following behaviour demonstrates how the daylight savings value gets
lost when a time value gets turned into an internal array of numbers and
then back into a (struct tm):

        $ TZ=Europe/London ./jq -r -n '1504803635 | strflocaltime("%Y-%m-%d %H:%M:%S (%Z)")'
        2017-09-07 18:00:35 (GMT)

After this change however, this works as expected:

        $ TZ=Europe/London ./jq -r -n '1504803635 | strflocaltime("%Y-%m-%d %H:%M:%S (%Z)")'
        2017-09-07 18:00:35 (BST)

src/builtin.c

@@ -1239,7 +1239,8 @@ static jv tm2jv(struct tm *tm) {
                   jv_number(tm->tm_min),
                   jv_number(tm->tm_sec),
                   jv_number(tm->tm_wday),
-                  jv_number(tm->tm_yday));
+                  jv_number(tm->tm_yday),
+                  jv_number(tm->tm_isdst));
 }
 
 #if defined(WIN32) && !defined(HAVE_SETENV)
@@ -1460,12 +1461,9 @@ static int jv2tm(jv a, struct tm *tm) {
   TO_TM_FIELD(tm->tm_sec,  a, 5);
   TO_TM_FIELD(tm->tm_wday, a, 6);
   TO_TM_FIELD(tm->tm_yday, a, 7);
+  TO_TM_FIELD(tm->tm_isdst, a, 8);
   jv_free(a);
 
-  // We use UTC everywhere (gettimeofday, gmtime) and UTC does not do DST.
-  // Setting tm_isdst to 0 is done by the memset.
-  // tm->tm_isdst = 0;
-
   // The standard permits the tm structure to contain additional members. We
   // hope it is okay to initialize them to zero, because the standard does not
   // provide an alternative.

tests/jq.test

@@ -1440,7 +1440,7 @@ bsearch(0,2,4)
 # strptime tests are in optional.test
 
 strftime("%Y-%m-%dT%H:%M:%SZ")
-[2015,2,5,23,51,47,4,63]
+[2015,2,5,23,51,47,4,63,0]
 "2015-03-05T23:51:47Z"
 
 strftime("%A, %B %d, %Y")
@@ -1449,7 +1449,7 @@ strftime("%A, %B %d, %Y")
 
 gmtime
 1425599507
-[2015,2,5,23,51,47,4,63]
+[2015,2,5,23,51,47,4,63,0]
 
 # module system
 import "a" as foo; import "b" as bar; def fooa: foo::a; [fooa, bar::a, bar::b, foo::a]

tests/man.test

@@ -645,7 +645,7 @@ fromdate
 
 strptime("%Y-%m-%dT%H:%M:%SZ")
 "2015-03-05T23:51:47Z"
-[2015,2,5,23,51,47,4,63]
+[2015,2,5,23,51,47,4,63,0]
 
 strptime("%Y-%m-%dT%H:%M:%SZ")|mktime
 "2015-03-05T23:51:47Z"

tests/optional.test

@@ -3,14 +3,14 @@
 # strptime() is not available on mingw/WIN32
 [strptime("%Y-%m-%dT%H:%M:%SZ")|(.,mktime)]
 "2015-03-05T23:51:47Z"
-[[2015,2,5,23,51,47,4,63],1425599507]
+[[2015,2,5,23,51,47,4,63,0],1425599507]
 
 # Check day-of-week and day of year computations
 # (should trip an assert if this fails)
 # This date range
 last(range(365 * 67)|("1970-03-01T01:02:03Z"|strptime("%Y-%m-%dT%H:%M:%SZ")|mktime) + (86400 * .)|strftime("%Y-%m-%dT%H:%M:%SZ")|strptime("%Y-%m-%dT%H:%M:%SZ"))
 null
-[2037,1,11,1,2,3,3,41]
+[2037,1,11,1,2,3,3,41,0]
 
 # %e is not available on mingw/WIN32
 strftime("%A, %B %e, %Y")