Fix portability of strptime especially for Windows (#3342)

tests/optional.test

@@ -1,18 +1,6 @@
 # See tests/jq.test and the jq manual for more information.
 
-# 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]
-
-# 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]
-
-# Regression test for #3276
+# Regression test for #3276 (fails on mingw/WIN32)
 fromdate
 "2038-01-19T03:14:08Z"
 2147483648
@@ -22,4 +10,3 @@ strftime("%A, %B %e, %Y")
 1435677542.822351
 "Tuesday, June 30, 2015"
 
-